Queltrax, Welkin Fiend

Flying, fear
Frantic (As you cast this spell, you may exile up to
X cards from the top of your library, where X is the
amount of generic mana in this spell's mana value.
This spell costs {1} less for each card exiled this way.)
At the beginning of each end step, each player
exiles the top X cards of their library, where X is
the total life all opponents have lost this turn.