THese are all pretty pushed. I remember when red and black couldn't get 2/2 for 2 without a downside. Now red gets them with haste and an optional kicker and black gets... I mean dang, that's a solid creature turn 2. Blue's till not there, but I'd gladly trade in a point of toughness for flash and flying... and more.
Is there going to be a green one? Perhaps since werewolves are dominating right now everybody else gets an "adversary"? Will we see a Howling Adversary in Crimson Vow?

Intrepid seems kind of insane. Don't like that it wasn't a classless human to fit with the others. I mean, vampires on innistrad usually get class and the red one didn't.

Spectral is good for what it costs

The multikicker on Tainted seems a bit high but the base creature is so intense for its cost I'm not sure it matters.

Bloodthirsty is just... weird. It's a fine 2-drop, haste bear and all, but kind of a lackluster 5, but kind of good again at 8?

I wonder how often you'd want to use Bloodthirsty adversary to recur a combat trick to target itself. If you kick it it'll be a 3/3 and the haste let's you get the drop on somebody. Throw a combat trick on there and it might just be worthwhile. Or you can get a kill spell. Or both?

love when mythics just get bonus stats for no reason. really strong design principles.

Could be a limited vs constructed thing. This is how good a French vanillas stats have to be to get played in standard out of context

Messed up thing is I’m unsure any of these will be played in T1 decks in standard. Great in limited, but in standard you’re getting meh value at each stage. Cost flexibility is their greatest asset and it’s not obvious to me that it’s enough

They gave green a rare grave titan so I don't really feel like the limited argument applies.

Wording wise, I feel like they should have been templated as "When ~ enters the battlefield, you may pay [mana] one or more times. When you do, [...]" instead of this really awkward "when you pay this cost one or more times".

the red and black ones seem like they could be playable depending on the format. The red one is only realistically going to be kicked once or not at all but both halves are pretty playable in theory, if not super pushed. The black one is pretty decent as a 2-drop but doesn't scale as much as the red one does. 7 points of power for 5 mana isn't bad though.

What exactly are the phasing rules anyway? Is it like flickering except you don't lose counters / attachments and it doesn't trigger enters / leaves the battlefield effects?

A phased out permanent never leaves the battlefield, but it and everything attached to it are treated as though they doesn't exist until its controller's next untap step, before they untap.

It never becomes a new object like something does when it gets flickered, so the phased out permanent will return with all its counters and auras and equipment still on it.

I've seen it described as "imagine you're putting a bowl over the whole card and everything on or attached to it". It's like it just isn't there but it doesn't go anywhere else. Then when it phases in, you remove the bowl.