Dreamkiller Succubus

Flying
Whenever Dreamkiller Succubus blocks or
becomes blocked by a creature, that creature's
base toughness is 1 until end of turn.
Whenever a creature with toughness 1 dies,
surveil X, where X is that creature's power.(Look
at the top X cards of your library, then put any
number of them into your graveyard and the rest on
top of your library in any order.)