Skeleton Scavengers enters the battlefield with a +1/+1 counter on it.
Pay
for each +1/+1 counter on Skeleton Scavengers:
Regenerate Skeleton Scavengers
(The next time this permanent would be destroyed this turn, it isn't. Instead tap it, remove all damage from it, and remove it from combat.). When it regenerates this way, put a +1/+1 counter on it.