La'brugh, the Maniacal
Some sort of Exiles purity.*
5 cost, 12 morale
At the end of your turn, if you have no cards left in your deck you gain 10 morale and your opponent loses 10 morale.**
Exhaust, pay 3, remove the top card of your deck from the game: Destroy target character on the battlefield.***
*Initially I wanted it to be Exiles OR Verore, a la Vasir, but then I decided that there ought to be a greater purity restriction than that. Perhaps Exiles And Verore, or double or triple Exiles. The idea is that CARDNAME is another archdemon from Torment like Vasir and Nysrugh (and presumably Tygrugh).
**This is an obvious homage to Lab Maniac in MtG, and the 10 morale gain is meant to counteract the loss you get when you run out of cards (so you'd be netting 0). Could also be rewritten as "if you have no cards left in your deck your opponent loses 10 morale instead of you," but I felt this would be easier to implement and understand.
***I felt that just having the alt win-con on him wouldn't be very fun or useful, but this way you'd want to run him in command since he's a deathray on a stick. While most repeatable activated abilities cost more than their once-off ability cards (Daode vs Daode's Protection, for instance), CARDNAME isn't garnering any card advantage because it costs you cards to use his ability. I chose to have him remove the card from the game rather than just put it into the graveyard because then you can't ditch a good card and just recycle it (woot for Exiles RNG adding risk). Perhaps I costed the ability too conservatively, but I try to err on the side of caution in these design challenges.