Proliferate
Keyword actions
Add one more of each kind of counter already present.
How it works
To proliferate, choose any number of permanents and/or players that already have a counter on them. For each one you chose, give it one more counter of each kind it already has.
Proliferate never adds a counter type that isn't already there — it only multiplies what's present.
Common confusions
“Can proliferate put a +1/+1 counter on a creature that has none?”
No. The permanent must already have at least one counter; proliferate then adds one more of each kind it has.
“Which counters can it touch?”
Any kind — +1/+1, -1/-1, loyalty on planeswalkers, poison on players, charge, oil, etc. You choose which permanents/players to include.
“A creature with both +1/+1 and -1/-1 counters.”
It shouldn't have both for long — equal numbers of +1/+1 and -1/-1 counters are removed in pairs as a state-based action before you'd usually proliferate.