[+1]: Until your next turn, whenever a creature deals combat damage to Vraska the Unseen, destroy that creature. [–3]: Destroy target nonland permanent. [–7]: Create three 1/1 black Assassin creature tokens with "Whenever this creature deals combat damage to a player, that player loses the game."
Wayfaring Temple's power and toughness are each equal to the number of creatures you control. Whenever Wayfaring Temple deals combat damage to a player, populate.
{1}, {T}, Discard a card: Put a study counter on Grimoire of the Dead. {T}, Remove three study counters from Grimoire of the Dead and sacrifice it: Put all creature cards from all graveyards onto the battlefield under your control. They're black Zombies in addition to their other colors and types.
{T}, Discard a card: Up to one target creature can't be blocked this turn. Whenever Key to the City becomes untapped, you may pay {2}. If you do, draw a card.
It would be unfortunate if the key fell into the wrong hands.
Imprint — Whenever a nontoken creature dies, you may exile that card. If you do, return each other card exiled with Mimic Vat to its owner's graveyard. {3}, {T}: Create a token that's a copy of a card exiled with Mimic Vat. It gains haste. Exile it at the beginning of the next end step.
When this creature enters, you may search your library for a basic land card, put that card onto the battlefield tapped, then shuffle. When this creature dies, you may draw a card.