MTG Salvation

The aura adds an activated ability to the land. Since both that and the inherrent mana ability of the land are activated abilities that require tapping the land, you can only pay for one with one tap. So you have to choose between mana or damage.

Now if it were to add a triggered ability, then you could get both by tapping the land for mana, and getting the damage from the trigger. But this is not how Noxious Field works.

Also note, that enchanting another player's land with that aura gives them, as the controler of the land, control over the damage ability. You can't tap their land like that.

Protection helps against four specific things (DEBT):
D amage to the object is prevented
E nchanting/equipping is not possible
B locking is not possible
T argeting is not possible

Protection is taken into account constantly at every time. Whenever something tries to do one or more of the four things, protection applies and stops it. In regards to abilities, the game looks at the source to determine if protection applies.

So in your first scenario, your Angelic Curator will not be tapped by Abyssal Hunter due to having become an illegal target. And since the ability doesn't resolve, the damage prevention doesn't even matter.

In your second scenario, you cannot target the Curator with the Souleater's ability due to protection from artifacts. To do so, you have to FIRST turn the Souleater into a nonartifact. Afterwards you can target the Curator at your leisure.

You'll make 5 token copies of the Chancelor. All of them trigger, then the legend rule makes you choose one of your 6 Chancelors to keep and the rest are put into the graveyard, thus not counted for the 5 triggers. After that, the triggers go on the stack, and when they resolve, they count the number of creatures you control at that moment. So yes, the later triggers will generate more tokens, because of the tokens created by the earlier triggers. Do note, that all players can interrupt this cascade by adding or removing creatures under your control.

Your second question doesn't make any sense, since Akoum Battlesinger only cares about Allies entering the battlefield, not goblins. There are no triggers here.

Edit:
Oops, somehow I thought the Chancelors were legendary. My bad.

Nothing says to untap the creatures. If the thing preventing them from untapping is gone, they will untap the next time they normally would, so in their controller's next untap step. Note, that untap effects can untap the creatures even with the Raiders on the field, because those only prevent untapping in the untap step.

Essentially, yes.

Here's the relevant rule

113.7a Once activated or triggered, an ability exists on the stack independently of its source.
Destruction or removal of the source after that time won’t affect the ability. Note that some
abilities cause a source to do something (for example, “Prodigal Pyromancer deals 1 damage to
any target”) rather than the ability doing anything directly. In these cases, any activated or
triggered ability that references information about the source for use while announcing an
activated ability or putting a triggered ability on the stack checks that information when the
ability is put onto the stack. Otherwise, it will check that information when it resolves. In both
instances, if the source is no longer in the zone it’s expected to be in at that time, its last known
information is used. The source can still perform the action even though it no longer exists.

Yes, you can respond to the upkeep trigger that phases your lands out by tapping your lands for mana. You have to use that mana in that upkeep step, though, since it will be emptied from your mana pool when the step ends.

Both buyback and Gandalf's trigger are trying to replace the same event (the spell being put into the graveyard when it is finished resolving). As the controller of the affected object you get to decide which replacement effect to apply first. The other will then no longer be applicable, and your choice of replacement will be carried out.

No, 4 mana is what you get. Or 3 if you activate the land's original mana ability. The original mana ability and the mana ability granted by Grafted Growth do not combine, you have to decide which one to activate, the other you can then not activate. Because the cost of tapping the land can no longer be paid, it was already tapped for the other ability. Market Festival then adds 2 mana to what the ability you activated produced.

Yes. The source of the damage isn't around anymore, so the game uses last known information about it to determine the results of the damage is deals. This LKI includes it having deathtouch, so any creature receiving damage from it will be destroyed by state based actions once the trigger has finished resolving.

113.7a Once activated or triggered, an ability exists on the stack independently of its source.
Destruction or removal of the source after that time won’t affect the ability. Note that some
abilities cause a source to do something (for example, “Prodigal Pyromancer deals 1 damage to
any target”) rather than the ability doing anything directly. In these cases, any activated or
triggered ability that references information about the source for use while announcing an
activated ability or putting a triggered ability on the stack checks that information when the
ability is put onto the stack. Otherwise, it will check that information when it resolves. In both
instances, if the source is no longer in the zone it’s expected to be in at that time, its last known
information is used. The source can still perform the action even though it no longer exists.

702.2e If an object changes zones before an effect causes it to deal damage, its last known
information is used to determine whether it had deathtouch.

This term "embedded trigger" doesn't exist in magic. Itzquinth has a reflexive trigger.

Roaming Throne doesn't work with reflexive or delayed triggers. The Throne looks for triggered abilities of creature permanents. Not triggered abilities of abilities.

603.2e Some effects refer to a triggered ability of an object. Such effects refer only to triggered abilities the object has, not any delayed triggered abilities (see rule 603.7) that may be created by abilities the object has.

603.12. A resolving spell or ability may allow or instruct a player to take an action and create a triggered ability that triggers “when [a player] [does or doesn’t]” take that action or “when [something happens] this way.” These reflexive triggered abilities follow the rules for delayed triggered abilities (see rule 603.7)

From playing a bunch, The Akroan War is a fine sweeper that won't kill your stuff. It's slow against a plain horde, but many decks rely on synergy. Consider what happens to an aggressor when you take their Mayhem Devil or Anax. Teach your opponent's creatures how to crew a chariot, spread the love!

From The Brothers' War, I'll be trying Rootwire Amalgam over a pair of Regisaur Alpha. I have high hopes even though it's only stats. I'd love to replace Scavenging Ooze if Greasefang ever dies out. Teferi, Temporal Pilgrim may be a midrange/control smasher. Obliterating Bolt is an upgraded Lava Coil.

EDIT: Jan 23. Current list is -1 Otawara, -1 Sokenzan, -2 Regisaur, -2 Mythos, -1 Ooze, -1 Abrade, +2 Rootwire Amalgam, +4 Ledger Shredder, +2 Spikefield Hazard. Shredders for staying alive and Hazards for killing Llanowar Elves.

If you want to go Historic, it's all about Soulherder. 1's and 2's, even the non-synergistic Thraben Inspector, get stronger with it. Historic also has Cloudshift. For Explorer, I would start with these changes:
-4 Justiciar's Portal
+4 Essence Flux
Flux is cheaper.
-3 Cloudkin Seer
-1 Inspiring Overseer
+4 Reflector Mage
All the 3's do the same thing. Reflector Mage is obnoxious with Metamorph and works immediately.
-4 Dawnbringer Cleric
+4 Professor of Symbology
Professor is worse at stopping them, but better at pushing you. This is just my preference.

Keep Whirler Rogue and Cloudblazer in mind if you want to go bigger, and Spirited Companion to go smaller. I don't know if there are too many 3's or blink spells.

EDIT: For the event, might as well use Razortide Bridge in the lands as a copy target versus removal-heavy decks. I tried an Ingenious Smith build a few times, but found it wanted to animate, not blink.

I tried The Elder Dragon War and it was a liability. I couldn't time any of the modes effectively. Fable has been good against everything but the most aggressive decks, and even then it sometimes auto-wins.

From playing a lot, I like instant, varied interaction (including Scavenging Ooze) and a flow of post-Chariot creatures to keep it crewed. Blue cards deal with broken stuff. Big stuff overpowers. Less intense mana requirements let the deck get away with some Pathways.

LATE, LATE EDIT:
I've run into issues with Multiple Choice and Gnarled Professor. Choice has done little because I use Borrower for bounce. It overpowers boards that a 4/4 is already overpowering. Beyond that, both are fine, but they rarely push the game in a different direction (go over the top, answer a Witch's Oven before it takes over, and so on). Cutting Professor makes it easier to run pathways and utility lands, Boseiju, Who Endures in particular.

I've had success with three cores for this deck. All start with 4 Fable, 4 Chariot, and each has 4 Bonecrusher.

The first adds Terror of the Peaks and 2-3 of an additional copier. Terror is only a little flimsy, enhances tokens, and ends the game as a token. I started using it after BR midrange decks picked up Sheoldred, the Apocalypse, making Gargaroth a lot weaker, and it really fits the "If I untap with this, I win" philosophy. I consider Scavenging Ooze essential to fight Greasefang, Okiba Boss, as the deck can't rely on drawing enough interaction to answer it multiple times. Other than that, I use Abrade, Brazen Borrower, and Spell Pierce. Slow them down, do something strong. It's powerful, but not as consistent, though Fable helps a lot. Fires of Victory is also a fine option, killing early x/4's. Opposing Liliana of the Veil has been a great target for Mythos of Illuna.

The next uses Briarbridge Tracker and Shark Typhoon as tokens, and attempts to keep the board clean and defend Reflection or Chariot on turn 5 with two-mana interaction. I like Negate and a mix of Fires of Victory and Abrade. I've yet to try Make Disappear. Scavenging Ooze isn't necessary with the extra answers. This is weaker, but flexible. The tokens aren't strong, but the deck has a longer time to use them, and gets to keep its mana open more.

The last ditches blue for speed with Elvish Mystic and Llanowar Elves. Lovestruck Beast has enough support, and Reckless Rage becomes great removal. This is more for best-of-three, where RB midrange is king and often can't kill a dragon. Five mana and 2 draws on turn 3 is good.

First, see what you get matched up against. I tried some "cards I have" versions and faced tons of ramp, which I seldom see playing BG.

My major issues were speed and mismatched interaction. My sweepers didn't line up and I was overrun by focused decks. Pressure + bounce works against Ramp's superior Koma and Elder Gargaroth. I was a little slower than my opponents, so I needed to interact, but I couldn't close (go over the top or get my own gameplan going at the same time), so they had several turns to draw what they needed. I found myself drawing to Koma, if anything. Beyond that, all I can offer are ideas because I saw little variety over three days of playing.

I wanted to Stomp, Crusher, Chariot, then mop up. This sequence at 2-3-4 pushed me away from a potential ramp path and towards cheap interaction and adventures. You'll likely end up elsewhere, but my strategy was to have Lovestruck Beast and Crusher attack and crew while Brazen Borrower bounces what slips past small numbers of Strangle, Lava Coil, and Spell Pierce.

I've been disappointed with Field of Ruin in a Tireless Tracker deck. Noting the deck's early RR mana requirement, I cut it for Ketria Triome, then added what I have for mana, using shocklands sparingly for 14 total untapped-on-one sources. Botanical Sanctum and Hinterland Harbor are neither ideal nor terrible, I use them if I'm taking too much damage from shocks and need intense color requirements early. With all the key 4-costs, I'd rather take turn 1 off sometimes than use Sanctum. Since blue isn't in demand, one-cost U spells like Miscast alleviate blue Pathways. Untapped-on-two is important considering how much better Stomp is on curve.

Sweepers are awkward. Anger of the Gods is good against Cauldron Familiar and Mono Red, but they have some draws that naturally play around it. Outside of that, so many decks skip from 2 to 4 to 6 toughness. WG angels is based around Righteous Valkyrie and Collected Company, G ramps to Steel Leaf Champion and either Collected Company or Elder Gargaroth, U Spirits has countermagic, and decks like control and Indomitable Creativity don't care. Lava Coil has issues, but is faster. Chandra, Torch of Defiance is great if it clears the way for Koma, Hydroid Krasis, or Elder Gargaroth (which obliterates a lot of common decks) and invalidates whatever the opponent has done. Storm's Wrath hits most of the same things as Burn Down the House.

I used a couple Fable of the Mirror-Breaker as filler because I only have 3 Chariots and Professors, but it shined when casting a 4 and leaving up an inconspicuous Spell Pierce.

Multiple Choice's bounce was better when I was attacking. Quality doesn't matter when they need blockers. I want to bounce my own creature, but it hasn't come up yet.

Professor was good. I thought it would be too slow or ruined by 2 mana removal, but learning/drawing is helpful even against linear decks. I didn't want to play it on turn 4 or 5, though, preferring Chariot or casting two small spells. That's fine, but I also haven't set up any big turn 7 plays.

Bonecrusher is perfect in the deck.

Grave hate may be helpful depending on your queue. Scavenging Ooze is better in general, Cemetery Prowler survives Anger and bullies Graveyard Trespasser and The Wandering Emperor. I didn't face anything that made me want to stop and cast either.

Many decks I face only interact incidentally and rely on being difficult to interact with. They want your Angers to be bad and to force you to use Lava Coil in an inopportune way, which can lead to playing cards like Chandra, Torch of Defiance primarily for the ramp/cards rather than for the removal. You ramp into Koma not as a reaction to midrange, but as a proactive threat that happens to crush midrange. In either case, you cast Koma and win, but I like the second way of thinking while playing Best of One, or for maximizing a deck's theme like the existing Stomp-Crusher-Chariot-Choice line.

EDIT: I've been trying something closer to the original. Growth Spiral is excellent, setting up a turn 3 Chariot or Storm's Wrath. You cast more stuff, and it's something to do when your interaction lacks targets.

I only have 2 Multiple Choice, so I substitute in junk. Verdurous Gearhulk, Elder Gargaroth, and Workshop Warchief are okay, with Gargaroth being the best even though Vigilance is bad with Chariot. Shark Typhoon is a little worse, and Shifting Ceratops is poor. Mythos of Illuna is too fun for me to evaluate. Copying a Lovestruck Beast, then duplicating the token is outrageous.

WUB has its own legend that gets wacky with Echoing Equation—Raffine, Scheming Seer.

This was my process. I hope it's helpful.

Goldfishing , I had trouble connecting everything while drawing the right mix of land and spells. That could be a non-issue with Arena's shuffler. Biomathemetician, Sarulf's Packmate, and Decisive Denial looked weakest, while Kairi looked to ignore the premise of the deck, so I targeted them for replacement.

My first try involved Stormchaser Drake, Ledger Shredder, and Crash Through, swapping green protection for blue (Slip out the Back, You See a Guard Approach, and March of Swirling Mist), and being open to refactoring the mana for Blizzard Brawl. Maybe something is there, but while I intended to use March to protect Orvar, trigger it and Drake, and mess with the opponent, the deck wanted to drop its core (Fynn, Orvar, and Equation, as I see it) for the new "protect the queen" style, so that was scrapped. I also eliminated an Illuminator Virtuoso + Homestead Courage and Sejiri Shelter build for the same reason.

Since the deck relies on 4 and 5 mana spells and copies things, maybe some beef would work. Topiary Stomper and Esika's Chariot came in over Bio and Packmate. The deck is still producing mixes with no creatures, no big stuff, or a lazy Stomper. Tangled Florahedron replaces Headquarters, Glasspool Mimic over Kairi. Same problem. 3 Shigeki, Jukai Visionary and 2 Lair of the Hydra (more options for Orvar to copy a land) over Decisive Denial and 1 Boseiju. Things were clunky, but now the deck was running and wanted to find its core, so I was happy.

Now I can see land over Mimic or working in more big stuff like Kairi or Workshop Warchief, but the Shigeki's especially worked well for me in making Orvar and Equation shine, from blocking and ramping to digging and recovery. I wish I had more land and interaction, but the deck has a lot of parts. If the functions of Denial are needed, I would look to trim some protection spells for Blizzard Brawl, Florahedron for snow lands, and Mimic for Malevolent Hermit or Jwari Disruption. The idea is to get some efficiency or versatility to support the inflexible frame. Winterthorn Blessing would also be an option instead of Brawl.

I considered Jaspera Sentinel, Elvish Warmaster, and Gala Greeters instead of Bio, Packwolf, and Headquarters or Denial. The goal is to use cheaper creatures and more mana to make it easier to use a combination when drawn. Ultimately, I like cats and dinosaurs.

Yes. It transformed, and the Ghastly Mimicry on the other side was still overridden by the name and other characteristics of the Brutal Cathar.

701.28e Some triggered abilities trigger when an object “transforms into” an object with a specified
characteristic. Such an ability triggers if the object transforms and has the specified
characteristic immediately after it transforms.

You have understood correctly that the ability should have triggered: under C.R. 723.2d, a "nontoken creature" includes a merged creature even if one of its components is a token, as long as its topmost component is not a token. If such a creature is not treated as a "nontoken creature" for the purposes of Nightmare Shepherd, then that is a bug in MTG Arena.

By the way, where Nightmare Shepherd says "it" (as in "you may exile it"), what is meant is the cards and tokens that make up the creature referred to (but note that any token components of that creature will have ceased to exist in the meantime [C.R. 704.5e]) (C.R. 400.7d, 400.2, 723.3c).

EDIT (Sep. 16; Oct. 3): Some rules were renumbered in the meantime.

In both cases, X/X (3/3 in your example).

In both cases, the "enter the battlefield as copies" replacement takes precedence over the "enters the battlefield with counters" replacement effect (C.R. 616.1c, 616.1e, 614.1c). As a result, Stonecoil Serpent's copiable values will be replaced with those of the chosen creature (see also an example in C.R. 616.1e). And the latter include the ability "Stonecoil Serpent enters the battlefield with X +1/+1 counters on it" in both cases. Now we apply the new replacement effect from the latter ability (C.R. 616.1e). Since the newly acquired ability has an "enters-the-battlefield ... replacement effect [that] refers to X" (C.R. 614.1c), the X on that ability is the same as the spell's (C.R. 107.3m), so the creature will enter the battlefield with X +1/+1 counters on it.

EDIT: Struck out certain text after comment 8 was posted. See comment 4.