This card will reshape Vintage. Young Pyromancer is already the bee's knees, and this ability is much more powerful than Young Pyromancer's. Not just because the tokens have prowess, but also because random artifacts can trigger it instead of just instants and sorceries.
On turn two you have three creatures with prowess, and with a couple more cantrips or Moxen that means attacking for 10 damage. Start throwing around more free spells like Gush and Gitaxian Probe, not to mention Time Walk, and it's not inconceivable to put together a turn-two kill. While a turn-one Young Pyromancer can develop an overwhelming board state, it isn't actually lethal to the opponent until turn four or so.
With a Mentor and a single token to hit the opponent with, every spell cast is essentially a copy of Tendrils of Agony. Only instead of losing value on a non-lethal Tendrils, you're gaining value like it's an Empty the Warrens.
One thing I really like about Mentor is that if it gets Bolted that doesn't remove prowess from the tokens. Again, this is much more powerful than what Young Pyromancer leaves behind.
This deck is built to take advantage of the differences between Mentor and Young Pyromancer, embracing the artifact plan and allowing for a wider range of busted openings.
Balance seems awkward with Mentor, and it is, but there will be games where you don't land a Mentor or it gets countered and the opponent generates a Young Pyromancer army or simply Tinkers up a Blightsteel Colossus. If Mentor is going, it should be winning, and if Mentor is absent then Balance should be good. Also, the more mana-centric the deck, the more it wants Balance because drawing it turn one alongside some artifact mana can Mind Twist the opponent out of the game.
I like how savvy sequencing with Sensei's Divining Top can convert extra mana into damage. Tap Top, play a cantrip, replay Top, repeat. Even simply drawing with Top before the normal draw every turn generates a lot of damage over a few turns. Again, this is not an interaction with Young Pyromancer, and it's one of the reasons Mentor is better despite costing one more and being in a generally worse color.
From the sideboard, playing and flashing back a Cabal Therapy overruns the team. This is much more exciting than the free 1/1 from Young Pyromancer.
Going forward, I imagine the main thing that'll need tweaking about this deck is the ratio of gas to mana, which can be tricky to balance in a deck full of artifact mana and Gitaxian Probes. I wouldn't be surprised if some number of cheaper cantrips needed to be cut for more powerful spells like Thirst for Knowledge or Fact or Fiction.
My main question for Mentor isn't how good it'll be in Standard and Vintage, as I have a pretty good idea on those fronts. Rather, I'm having a difficult time seeing where it fits into Modern and Legacy, where there isn't the same kind of time to set up that we have in Standard or the fast artifact mana of Vintage. If it only sees play in tempo decks, the extra mana matters a lot more and Young Pyromancer is probably still the better card, and a list starting 4 Delver of Secrets 4 Young Pyromancer 2 Mentor sounds best.
Outside of tempo, it can't really replace True-Name Nemesis because the two cards aren't doing the same thing. Even if Mentor is more powerful than True-Name, True-Name is still blue instead of white, and in Stoneforge Mystic decks it's better at carrying equipment.
That said, Legacy has cards like Cabal Therapy, Sensei's Divining Top, Chrome Mox, and Lotus Petal. I can imagine a successful 4x Mentor list wanting some combination of these cards, though I'm not sure what that deck would look like.
Soulfire Grand Master
While it should see some play in Standard, this card is tremendously overhyped in general. Yes, it combines with Time Walk (and six mana) to generate infinite turns, but that's a lot of mana, a vulnerable 2/2 body, and requires not having used said Time Walk already.
Don't get me wrong, I understand the hype. Currently, an infinite-turns loop is all the rage in Vintage, and standoffs can happen where players sit around with piles of mana. At first glance, I can see why people would get excited.
The main difference is that Time Vault + Voltaic Key only costs four mana total and can be spaced over multiple turns. Blue can tutor them directly into play with Tinker. And if we were looking for wonky two-card combos, we could always turn to stuff like Helm + Rest in Peace or Painter + Grindstone or Auriok Salvagers + Black Lotus. Even if taking extra turns is the best way to win the game, that isn't why Vault + Key is so heavily played, but rather because it's the most efficient win available. If combining the two dealt each opponent 20 damage it'd still see the same level of play.
Soulfire shares none of the characteristics of other playable creatures in the format. How soon does Goblin Welder do something relevant? Aven Mindcensor might cost 3, but it has a chance to win you the game long before Soulfire comes online. How often were you combining Time Walk with Young Pyromancer or Dark Confidant and losing the game? And that's four mana when cast on the same turn—Soulfire is a whopping eight.
In Vintage, if I need 5-6 mana for something to be good, that something needs some pretty strong advantages. Mind's Desire needs 3ish other spells, but they can be any other spells, and it's very likely to win the game on the spot. Yawgmoth's Bargain doesn't need much of anything to win that turn. Soulfire Grand Master specifically needs Time Walk to win, and there'll be games where combining it with Lightning Bolt or Mana Drain isn't enough.
When I went over the set mechanics a few weeks ago, I speculated that a blue manifest Aura that gave hexproof might be interesting enough to make Phyrexian Dreadnought worth trying again.
Well, it's here, and it complements Dreadnought's weaknesses so well that it is indeed interesting enough to be worth testing. It can be Abrupt Decayed, but then they still need another answer for the Dreadnought itself.
Here's my first crack at it:
Why this over Rest in Peace + Helm of Obedience? There are a lot of reasons, starting with the fact that Cloudform pitches to Force of Will. On top of that, Cloudform is a bit more useful on its own than Helm of Obedience, and Dreadnought also combines with Stifle. Don't think of Cloudform and Dreadnought as a wonky two-card win condition, think of it as a more resilient endgame for the existing Stiflenought combo.
One neat thing about the combo is that you can use Brainstorm or Jace to set it up. In fact, the nut draw is something like turn-one Brainstorm (putting Dreadnought two deep), turn-two Chrome Mox into Cloudform.
You can use Enlightened Tutor to set it up on turn three, but you also need a turn-one Sensei's Divining Top so that you can use your turn two to Tutor + Top, moving the Dreadnought so that you don't natural-draw it on turn three.
Without a Top, you need to save the Tutor for the same turn you Cloudform, or use it to tutor for Cloudform itself if you already have Brainstorm + Dreadnought or simply another Enlightened Tutor. Since Tutor + Cloudform costs a whopping four mana, I like the miser's Chrome Mox as a way to potentially speed things up. By the same logic, Daze is way too harsh on the curve.
Historically, Enlightened Tutor starts as a 4-of in this style of deck and then becomes a 3-of and so on down to 0-of. Here, I'm starting with 4 because it's so specifically good at setting up same-turn Cloudforms, but if it ends up being too clunky then I'd like to cut them to make room for a Stoneforge Mystic package.
Stoneforge Mystic not only ups the threat count of the deck, but it also makes use of a random hexproof flying 2/2. In this sense, Cloudform could be half Illusionary Mask half True-Name Nemesis, which seems pretty good.
I don't think Cloudform is going to become tier any time soon. However, some build with it might be somewhat competitive, and the idea is fun enough that that's worth it for me.
Frost Walker's Illusion ability is a non-factor in that anything your opponent will target it with (Lightning Bolt, Red Elemental Blast) would kill it anyway. It does come up if you ever want to suit it up or jump it with an Elspeth or something.
At one point, Dandan was a viable sideboard card in Vintage, mostly for sweet blue mirrors where no one actually had a removal spell post-board. In the current day of Young Pyromancer tokens, Darkblast, and Slice and Dice it looks much worse. That said, the current metagame won't exist forever, and I could see a 2-mana 4/1 with basically no downside being played in potential Modern or Legacy metagames as well, if only as a niche sideboard card for wonky control mirrors.
Losing it to a Maze of Ith sounds like the worst thing ever.
Marang River Prowler
Too clunky for Legacy, and probably Modern as well, but if it fits in anywhere it'd be in Modern Dredgevine. Casting a creature from the graveyard is particularly good at triggering the deck's namesake, and the deck should be filled with green and black bodies anyway.
When compared to the efficiency of Gravecrawler, it's hard to justify the cost.
We've got another dud, folks. After the initial hype wears off, this should see approximately no play.
Anyone that has messed around with Dead Drop in Standard knows that ten is already a ton of mana, even with delve, and Trespass costs eleven. On the low end, UUU is a lot to pay after exiling your entire graveyard.
They had to make it this way, since an undercosted Time Walk effect would be broken.
This guy is probably too vulnerable to see play in Modern, but that's the format where you have the tools and room to play the "how many times can I untap this guy" game. Just put the ability on the stack, respond with something to untap it, and then put the ability on the stack again. The downside is that if you let the Defector ability resolve, you can't use the cards you drew into to untap it again because the opponent will have control.
When it was first printed, there were versions of Ascendancy combo playing mana dorks and Cerulean Wisps. If Humble Defector finds a home in an Eternal format, it'll probably be in something like that.
Sacrificing him in response is also a fine play, though unless you have some way to reuse the ability it isn't worth it. There aren't many decks that want a more vulnerable Font of Fortunes, though if the deck was aggressive enough the 2/1 body could be a real benefit. Maybe some kind of Greater Gargadon shell?
It sounds just janky enough to work.