I'm not a fan of snow, so I'm not going to include anything that relies on snow. Without snow cards, this set was very weak. Fortell also loses some value if you only have a few cards with it. It's a good ability though so I hope it sees more use in future sets.
Murderous Cut feels like a 3 mana card most of the time (although it is sometimes great when you can play cut and another four mana spell with five land). Bloodchief's Thirst seems like a Disfigure with an overpriced Murder attached for the late game. Or is the sorcery speed too detrimental?
Well the full spoiler is up, but I didn't notice much more. I very much dislike Party as a mechanic so this set is pretty bad for me. I'm not supporting tribes so I want to avoid misleading players that I support tribal unless the card supports itself like Cloudgoat Ranger. The kicker cards and DFC also seem mostly weak this time around.
Cards I'm interested in: Fearless Fledgling - Wish it always had flying but it gets to a reasonable size quickly, especially if it comes down on curve. Bubble Snare - Contender for best Blue aura-based removal. The 1 mana mode is quite reasonable, and the backup 4 mana mode is only slightly over-costed. Malakir Rebirth - The most efficient DFC. Might replace Supernatural Stamina or Undying Evil Rockslide Sorcerer - Wish it was just non-creature instead of including wizards. Seems pretty strong though in the spell-slinger deck. Adventure Awaits - Whiff insurance is the only reason this interests me. Bala Ged Recovery - Regrowth at 3 mana still seems reasonable. Green decks are usually the most land-hungry decks. Gnarlid Colony - Another decent but not particularly strong +1/+1 counter support card.
I'll need to think about these more but I wouldn't be surprised if only 2-3 of these make it into my cube.
Sentinel of the Eternal Watch will definitely age poorly once we get more playable white finishers (though white having some recursion/protection will probably keep it relevant for a good while). Waker of Waves is in the same "can't die while this lives" category and it got a pretty lukewarm response since we actually have good blue high end.
It feels like it could be a decade before we finally get a decent fatty to replace the Sentinel. Looking on Scryfall, there's only 73 mono-W creatures at 6+ cmc. Most are pretty bad. They've been printing them a bit more frequently in recent sets, so maybe there's hope.
Also Serra Sphinx and Skullmulcher. If Green is a go-wide color in your cube Skullmulcher might be worth it. 5 mana and sac two 1/1 tokens to get a 5/5 and draw two cards seems pretty good, but that could be hard to hit consistently except in a very token heavy deck.
Since the downshifts were pretty boring this masters set, and I'm bored myself, I went through the list of rares and mythics to see what could have easily been downshifted, and what would have been possibly okay to downshift but possibly too good:
Easy Downshifts:
Boon Reflection - I don't think this or the lifegain archetype in Peasant is very good, but why not give us the option?
Thought Reflection - A 7 mana enchantment that does nothing to affect the board. Maybe control decks would want this?
Doomed Necromancer - A creature version of Zombify, same total mana cost and all. There are creature shenanigens that can give you upsides over Zombify, but Doomed Necromancer also takes 2 turns typically, so I don't see him being that much better.
Heat Shimmer - We have Mirror Image for a 3 mana 1-sided clone, and the original Clone at 4 mana. So a 3 mana clone in red that lasts only 1 turn seems fine to me.
Ion Storm - This just seems bad. I doubt it would see any play but it still should have been downshifted.
Hanna, Ship's Navigator - The body is terrible and it's just really slow. I also doubt this would see play but it would have been nice to at least have the option.
Phyrexian Revoker - A nice utility hate creature. There's probably not enough scary activated abilities to make this maindeckable, but it might be nice sideboard card to pick up later in a draft.
Spicy downshifts that would be nice but maybe too good:
Beacon of Unrest - Hitting both graveyards and both artifacts and creatures at 5 mana is right on curve for peasant playability IMO. I'm not sure if shuffling back into the library changes things in 40 card decks though.
Magus of the Will - I'm guessing after you sac this guy you'll probably have 3-4 mana left in a good case, which usually probably equates to re-casting just 1 spell. He does have a good floor though as a 3 mana 3/3. I don't see much combo potential in the peasant cube environment.
Salvage Titan - Already discussed in this thread. In an artifact cube this could be super explosive but is also just as likely to a bad 6 mana creature.
Skirsdag High Priest - This card asks for a LOT of set-up to work. When it does work it can take over the game but I think there will also be a lot of games where this guy does nothing.
Cragganwick Cremator - Above curve but the random discard can either break your back or deal a ton of damage to your opponent's face just when you need it. I think this would be okay overall though.
Rage Reflection - 6 mana enchantment that does nothing without an established board. It will end games if your board is even near parity, and is also good on defense, so it may be too good.
Spiteful Prankster seems decent for aggro. 3 power first strike when attacking, and the ping ability provides reach when your small creatures start getting outclassed. Even triggers off of opponent's creatures.
EDIT: Just realized this is just a better Hissing Iguanar. Easy swap for me.
Maybes: Basri's Acolyte Basri's Solidarity - Fairly efficient permanent pump, and supports a +1/+1 counter theme. Sorcery speed might kill it though Swift Response - Simple and fairly efficient de-powered removal. Mistral Singer - Supports flyers and spellslinger but maybe a touch weak. Spined Megalodon - Big resilient beater, but it has to compete with Striped Riverwinder Waker of Waves - Super cycling is great, but it lacks the resilience on board. Also competing with Striped Riverwinder Alchemist's Gift - Nice flexibility for just 1 mana, but probably not worth a card Liliana's Devotee - Decent support for the BW sacrifice deck Malefic Scythe - It becomes good with just 1 death trigger. With 2+ it becomes great. Village Rites - Nice and efficient, but not sure if it edges out the other black draw spells Hobblefiend - One of the better Carrion Feeder type cards. Nice that it has evasion too and has a reasonable floor. Not sure if I want this in red though. Llanowar Visionary - Efficient but boring. Pridemalkin - Decent +1/+1 Counter lord, but a bit weak by itself. Experimental Overload - Seems good with just 3 instants/sorceries in graveyard.
UW Flyers has come together nicely recently. Watcher of the Spheres is an auto-include for me! Only thing left the archetype needs is a mono-white flying matters card that is actually good.
I generally like to keep permanent hexproof to a minimum, and I'd even prefer other forms of resilience (like Jetting Glasskite, Warden of the Woods, Pelakka Wurm) that didn't shut down interactivity as much. Especially with our lack of good board wipes, generally only sacrifice effects work.
I'm considering replacing Skysnare Spider with Warden of the Woods. The Warden looks better at first glance but the spider's reach has saved me in a few games.
Hellkite Punisher is too expensive for no immediate impact or protection. Honestly even Shivan Dragon might not cut it these days if it were available. What I would be interested in is a better Volcanic Dragon
Bayou Barker, Plumb the Forbidden, Expressive Iteration, and Zephyr Boots also look a bit interesting but probably aren't good enough.
Definite Includes
Usher of the Fallen - As everyone else has said, standout card of the set
Snakeskin Veil - Supports my +1/+1 counter theme in green and a similar power-level to blossoming defense.
Maybe
Axgard Braggart - +1/+1 counters, can get big over time and pseudo-vigilance, are all nice, but probably too slow
Battershield Warrior - Supports white weenie/go-wide, but the floor is probably too low to be good
Battlefield Raptor - Probably the best 1-mana flyer in white? Good target for counters/auras/equipment
Bound in Gold - Possibly better than Faith's Fetters?
Wings of the Cosmos - One of the better combat tricks
Behold the Multiverse - seems good but is competing with Rain of revelation and Deep Analysis (both cards that I play), and Chemister's insight (which I don't)
Bind the Monster - Good removal but I think I prefer Bubble snare
Giant's Amulet - Good rate for both the creature and equipment
Ravenform - decent removal
Axgard Cavalry - might be better than the 1 mana 1/1 versions of this, but red 2 drops are pretty stacked now
Rootless Yew - seems good in a dedicated G/x ramp deck, but 6+ power or toughness is still a high bar to clear, only 11 creatures in my cube meet that.
Sarulf's Packmate - Good card but too similar to Llanowar Visionary
Kardur, Doomscourge - interesting effect, but not sure on power-level
Is the ranking for white 2/1 for 1 Dauntless Bodyguard > Usher of the Fallen > Skymarcher Aspirant = Mardu Woe-Reaper = Dryad Militant > everything else?
Personally the sorcery speed kills the card.
Cards I'm interested in:
Fearless Fledgling - Wish it always had flying but it gets to a reasonable size quickly, especially if it comes down on curve.
Bubble Snare - Contender for best Blue aura-based removal. The 1 mana mode is quite reasonable, and the backup 4 mana mode is only slightly over-costed.
Malakir Rebirth - The most efficient DFC. Might replace Supernatural Stamina or Undying Evil
Rockslide Sorcerer - Wish it was just non-creature instead of including wizards. Seems pretty strong though in the spell-slinger deck.
Adventure Awaits - Whiff insurance is the only reason this interests me.
Bala Ged Recovery - Regrowth at 3 mana still seems reasonable. Green decks are usually the most land-hungry decks.
Gnarlid Colony - Another decent but not particularly strong +1/+1 counter support card.
I'll need to think about these more but I wouldn't be surprised if only 2-3 of these make it into my cube.
It feels like it could be a decade before we finally get a decent fatty to replace the Sentinel. Looking on Scryfall, there's only 73 mono-W creatures at 6+ cmc. Most are pretty bad. They've been printing them a bit more frequently in recent sets, so maybe there's hope.
Easy Downshifts:
Spicy downshifts that would be nice but maybe too good:
Spiteful Prankster seems decent for aggro. 3 power first strike when attacking, and the ping ability provides reach when your small creatures start getting outclassed. Even triggers off of opponent's creatures.
EDIT: Just realized this is just a better Hissing Iguanar. Easy swap for me.
Shipwreck Dowser - Probably best version of the effect yet. Will replace Vexing Scuttler
Bolt Hound - Nice support for go-wide aggro, but it is a bit fragile. Probably replacing Breakneck Rider
Heartfire Immolator - Best card of the set IMO. Holding up mana to bluff or to cast a spell will make things very hard on your opponent.
Warden of the Woods - Strong on defense, and good value in the face of removal.
Watcher of the Spheres - Great flyers payoff. Replacing Aven Wind Guide
Maybes:
Basri's Acolyte
Basri's Solidarity - Fairly efficient permanent pump, and supports a +1/+1 counter theme. Sorcery speed might kill it though
Swift Response - Simple and fairly efficient de-powered removal.
Mistral Singer - Supports flyers and spellslinger but maybe a touch weak.
Spined Megalodon - Big resilient beater, but it has to compete with Striped Riverwinder
Waker of Waves - Super cycling is great, but it lacks the resilience on board. Also competing with Striped Riverwinder
Alchemist's Gift - Nice flexibility for just 1 mana, but probably not worth a card
Liliana's Devotee - Decent support for the BW sacrifice deck
Malefic Scythe - It becomes good with just 1 death trigger. With 2+ it becomes great.
Village Rites - Nice and efficient, but not sure if it edges out the other black draw spells
Hobblefiend - One of the better Carrion Feeder type cards. Nice that it has evasion too and has a reasonable floor. Not sure if I want this in red though.
Llanowar Visionary - Efficient but boring.
Pridemalkin - Decent +1/+1 Counter lord, but a bit weak by itself.
Experimental Overload - Seems good with just 3 instants/sorceries in graveyard.
If it's the main archetype for the color pair, then I think it makes sense to support it with many cards.
I've got Jubilant Skybonder, Thunderclap Wyvern, Warden of Evos Isle, Sprite Noble, and Favorable Winds all for this archetype. And now this new card.
I'm considering replacing Skysnare Spider with Warden of the Woods. The Warden looks better at first glance but the spider's reach has saved me in a few games.
Hellkite Punisher is too expensive for no immediate impact or protection. Honestly even Shivan Dragon might not cut it these days if it were available. What I would be interested in is a better Volcanic Dragon