Mesmer Ritual

Whenever a creature an opponent controls dies, mesmerise (Reveal the top X cards of your library,
where X is the number of creatures you control. Put
one of the revealed cards into your hand and the rest
at the bottom of your library in any order, then
shuffle.)
As long as you've revealed one or more cards
from the top of your library this turn, creatures
you control gain +1/+0 until end of turn.
If Mesmer Ritual would be put into exile from anywhere, put it into your hand instead.