Rivix, Seal Keeper

Haste, Deathtouch, Shadewalk(Whenever this
creature attacks a player, this creature and target
creature that player controls gain Shadow)
Whenever a creature dies, its controller creates
a Locus token. (It's an enchantment with "{t},
Sacrifice this enchantment: Add {c} and lose 1 life.)
At the beginning of your end step, each
opponent takes 1 damage for each Locus
they control.