Rosengar, Blood Ritualist

Bat, Demon, and Vampire creatures you control
get +1/+1 and have "Whenever this creature
deals combat damage to a player, you may pay
{b}. If you do, create a Blood token."
{b}{b}{b}, {t}, Sacrifice X Blood tokens: Search
your library for a Bat, Demon, or Vampire
with mana value X or less and put it onto the
battlefield tapped. Then shuffle your library.
Activate only as a sorcery.