Canker Abomination without a +1/+1 counter on it).
Notable Prerequisites
An opponent controls a creature.
Steps
Activate
Bartolomé del Presidio by sacrificing
Canker Abomination.
When
Canker Abomination dies, its undying ability triggers, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
When
Canker Abomination enters the battlefield, it triggers, putting a number of -1/-1 counters on it equal to the number of creatures an opponent controls.
If the opponent had seven or more creatures,
Canker Abomination will die as a state-based action due to having 0 or less toughness. If this occurs, repeat steps 2 through 4 infinitely.
Otherwise, resolve the
Bartolomé del Presidio ability, and repeat from step 1.