Feast for the Mind

Choose any number of creatures you control.
For each chosen creature, sacrifice it, then
return it to the battlefield under its owner's
control, except it's a Zombie in addition to its
other types and it has "At the beginning of your
upkeep, each opponent loses 1 life."
"The recruiting can get very messy here. My brother
once killed a Krelli cult member. He returned in time
for dinner, but he ate something very different."
-A Kessig villager, recounting his story