MTG Salvation

Priest has a replacement ability, not a triggered ability; Torpor Orb has no effect here. The creature will be exiled.

Yes to all three Qs.
A Dashed spell is cast like any normal spell, only the cost is different (aternative cost) and a delayed ability will trigger and (try to) return it to hand.

See rules 117.9, 603.7 & 702.108 for details.

Also, from Oviya's own rulings:

The value of X is determined only as Oviya Pashiri’s last ability resolves. The token’s power and toughness won’t change as the number of creatures you control changes.

No damage in either situation: the opposing player's creatures are exiled during Blockers Step, which happens before Combat Damage Step.

Danitha, being blocked and not having Trample, will not deal damage.

Do note that Scourge's abilities are not 'mana abilities'.
They do COST mana to activate, but mana abilities are those that PRODUCE mana. See rule 605 for details.

A very large number of activated abilities can usually be used only once, but that is only because their cost demand you TAP the creature, which can (normally) be done only once, and then wait for it to untap on your next turn.

Quote from BlazingRagnarok »

Entering the battlefield is specifically a zone change in which a card moves from a zone other than the battlefield to the battlefield.

When tokens are created, they do enter the battlefield, even though they did not move in from another zone.

This difference is fully justified:
'to attack' is an action, a verb: 'I do'
'to be an attacking creature' is a state, a condition: 'I am'

Lifeline returns no creature when Wrath of God kills them all simultaneously. False Prophet does nothing special in this case.
(unless some creatures had indestructible)

Quote from HandsomeP »

When the text on two cards instruct you (or seem to instruct you) to do something contradictory, which of the two take place?

As can be seen, the effects of cards often are sequential, so there is no doubt as to which one you'll obey: the first one to resolve. Yet, it is possible that you get contradictory and simultaneous instructions; rules 101.2 & 616.1 will resolve most of these conundrums:

Wow, couldn't you just rewrite it correctly? That's incredibly difficult to understand.

The latter.

In general, to pay for a crew ability, you must "[t]ap any number of untapped creatures you control with total power N or greater" (C.R. 702.121a). Thus, for example, to pay for crew 3, you choose any number of untapped creatures you control with total power 3 or greater, then tap those creatures at the same time (C.R. 601.2h). You can't tap a creature more than once to pay this cost (e.g., you can't choose just one creature with power 2 and tap it twice) (C.R. 118.10), nor can you activate any abilities (such as Duergar Mine-Captain's ability) while paying the cost of crew or any other spell or ability (you don't have priority to activate abilities while you're paying the cost of a spell or ability [C.R. 117.3, 117.1b, 601.2h]).

Yes

No, I did not miss that part. But that part refers to the replacement effects, and applies here only to the riot ability, which does only affect the permanent itself. Rhythm's ability however does not create a replacement effect, it grants an ability that then creates a replacement effect. And as I quoted above, continuous effects of static abilities of the permanent itself are taken into account.

This is different from the Orb of Dreams, where the ability itself creates the replacement effect.

Riot is not a trigger but a static ability creating a replacement effect which is applied as a permanent enters the battlefield. But since Rhythm of the Wild is not yet on the battlefield to generate that static ability, and replacement effects have to exist before the event takes place, it is too late to be applied to any permanent entering the battlefield alongside it.

Oddly enough, Rhythm of the Wild itself will benefit from riot, due to this rule:

614.12 Some replacement effects modify how a permanent enters the battlefield. (See rules 614.1c–d.) Such effects may come from the permanent itself if they affect only that permanent (as opposed to a general subset of permanents that includes it). They may also come from other sources. To determine which replacement effects apply and how they apply, check the characteristics of the permanent as it would exist on the battlefield, taking into account replacement effects that have already modified how it enters the battlefield (see rule 616.1), continuous effects from the permanent’s own static abilities that would apply to it once it’s on the battlefield, and continuous effects that already exist and would apply to the permanent.

This means, that you take into account the riot replacement effect generated by the Rhythms own riot ability granted by the static ability it would have once it's on the battlefield.

Assuming you own Sakashima in the graveyard, control Volrath's Shapeshifter entering the battlefield, and control Simic Guildgate on the battlefield:

Volrath's Shapeshifter's effect giving it "the full text" of a certain card (and additional text) is a continuous effect from a static ability. Here, this is a "continuous effec[t] from [Volrath's Shapeshifter's] own static abilit[y] that would apply to [Volrath's Shapeshifter] once it's on the battlefield" (because it would give Volrath's Shapeshifter "the full text" of Sakashima, including Sakashima's ability, and additional text once Volrath's Shapeshifter is on the battlefield), and this is one of the things that are "tak[en] into account" when determining "the characteristics of [Volrath's Shapeshifter] as it would exist on the battlefield" for the purpose of "determin[ing] which replacement effects apply and how they apply" (C.R. 614.12), and that includes, in this case, the replacement effect from Sakashima's ability as acquired by Volrath's Shapeshifter for this purpose.

Therefore, Volrath's Shapeshifter would take into account that it would enter with "the full text" of Sakashima (and additional text) in time to apply the replacement effect of Sakashima's ability acquired this way.

If you apply this replacement effect this way and you choose Simic Guildgate this way while it's a creature, Volrath's Shapeshifter will instead enter the battlefield as a copy of Simic Guildgate, "except its name is Sakashima the Impostor" (not any other name, including Volrath's Shapeshifter or Simic Guildgate [C.R. 201.4, especially C.R. 201.4b]), "it's legendary in addition to its other types, and it has '2UU: Return this creature to its owner's hand at the beginning of the next end step'", and it won't necessarily have the "full text" of a card in the graveyard even if that card is a creature card. Here is what happens in terms of the layer system:

• Original object (C.R. 613.1): Volrath's Shapeshifter has its usual text.
• Layer 1, copy effects (C.R. 613.1a): Volrath's Shapeshifter has the copiable values of Simic Guildgate, with certain exceptions, instead of its usual text (C.R. 706.2, 706.9c). Notably, Volrath's Shapeshifter no longer has the first ability set forth in its usual text, because the "copied information" overwrites Volrath's Shapeshifter's usual text (C.R. 706.3).
• Layer 2, control-changing effects (C.R. 613.1b): No relevant effects.
• Layer 3, text-changing effects (C.R. 613.1c): No relevant effects, especially because Volrath's Shapeshifter no longer has the first ability set forth in its usual text, due to the copy effect from layer 1.
• Layers 4-7 (C.R. 613.1d-g): No relevant effects.

EDIT (Jan. 20): Correctness edit.
EDIT (Mar. 21): Edited.

Savage Ventmaw's ability will trigger as soon as it's declared as an attacker; once it triggers, it will get to resolve even if it loses all abilities in the meantime (C.R. 113.7a). Thus, in this scenario, if your opponent wants Savage Ventmaw to lose its abilities before attackers are declared, they need to cast Polymorphist's Jest before you declare attackers, which they can easily do by saying, for example, "before you attack, I cast ..." (C.R. 500.2; see also this thread).

EDIT (Mar. 19, 2020): One rule was renumbered with Core Set 2020.

Quote from Rezzahan »

And in the case of an instant or a card with flash, you won't be able to snatch it period even if it's not a main phase or the stack isn't empty.

Excepting of course that Mulfrotha doesn't let you play instants

Quote from willdice »

I'm inclined to believe the mode can be chosen (as the game won't assume the effect is still impossible by the time the ability resolves), but I'd like something concrete confirming this.

So, I was all about ready to write a comforting post putting aside such preoccupations as just a sticky feeling from the word 'choose'. But, it seems that in Rules-As-Written, we actually can't pick the life-total option:

700.2. A spell or ability is modal if it has two or more options in a bulleted list preceded by instructions for a player to choose a number of those options, such as “Choose one —.” Each of those options is a mode. Modal cards printed prior to the Khans of Tarkir® set didn’t use bulleted lists for the modes; these cards have received errata in the Oracle card reference so the modes do appear in a bulleted list.
700.2b The controller of a modal triggered ability chooses the mode(s) as part of putting that ability on the stack. If one of the modes would be illegal (due to an inability to choose legal targets, for example), that mode can’t be chosen. If no mode is chosen, the ability is removed from the stack. (See rule 603.3c.)
603.3c [in evidence, post #6]

If "a mode would be illegal", then it can't be chosen. Not 'is', "would be". What makes a mode illegal? What IS a mode? A mode is an "option (among others) in a bulleted list preceded by instructions for a player to choose a number of those options". How can an option be illegal? Well, maybe because it, insofar as it is instructions, is impossible. There's certainly not enough basis for this nature to be wrapped up as "an inability to choose legal targets, for example". What were the other factors supposed to be? What else in 601.2 even makes a triggered ability ever subject to illegality, if that's what the gesture of the example is meant to say?
The word 'would' there is damning doubly so. Factors in Magic just -are- or aren't illegal. But the way text "would" work out, really, can only be thought to be the generation of effects, to a player who figures the words in the CR are chosen for reasons.

I wish I could have given my foolishly simple reply: