Fatestitcher
How would you change the mana costs on some of them then?
Apocalyptic Horde: A 5/4 for 5 in black is already really strong. I'd shrink it to maybe a 3/2 and up the cost to 7. Mass revival should be expensive.
Undying Horde: I'm not sure how undying plays yet, so it might be fair. But since it's all zombies you control, I might switch undying to persist.
Savra: Again, she'd be playable at that cost and size even if there was nothing in her text box. I'd shrink her to 4/4 and put her cost at 8, but even then she almost outshines Akroma.
Regretful Necromancer: Mana cost is fair, but 2 life is really cheap for a creature. Maybe 5 life, something that the player will notice.
No Escape: should be fine
Final Hour: If done right, this is a one-sided Wrath for 1 less than Wrath. Either up the cost (something like 6 should work) or lower the number of creatures destroyed by it (maybe half of the sac'd toughness)
Demonic Resurrection: This one might actually be overcosted, since most creatures won't survive an Infest.
Cloning Lab: At least require tapping.
Alduin: Shrink him, maybe to a 5/5. 7/7 for 7 in black is gigantic.
Dovahkiin: I think he'd end up dead before his ability is relevant a lot of the time. Help a brother out, give him first strike.
Two-color dragons: These seem pretty fun. Balanced attack triggers and fairly costed. Nice.