What it does
Bolster N means you find the creature you control with the least toughness and put N +1/+1 counters on it. If two or more creatures are tied for the least toughness, you choose among those tied which one gets the counters.
The big nuance: bolster isn't a targeted ability and doesn't let you freely pick any creature. You must put the counters on a creature with the lowest toughness—you only get a choice when there's a tie. This means hexproof and protection don't stop bolster, but it also means you can't always buff your best creature. If you have no creatures, bolster simply does nothing.
In Commander, bolster shines in +1/+1 counter and go-wide token decks, where it grows your board and triggers counter synergies. Just be aware it can accidentally pump a token instead of your bomb if that token has lower toughness.













