EvolveEvolve is a triggered ability. “Evolve” means “Whenever a creature you control enters, if that creature’s power is greater than this creature’s power and/or that creature’s toughness is greater than this creature’s toughness, put a +1/+1 counter on this creature.”
A creature “evolves” when one or more +1/+1 counters are put on it as a result of its evolve ability resolving.
A creature can’t have a greater power or toughness than a noncreature permanent.
If a creature has multiple instances of evolve, each triggers separately. (CR 702.100) (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1
counterTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) on this creature.)
Whenever one or more +1/+1
countersTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) are put on this creature, you may
createTo create one or more tokens with certain characteristics, put the specified number of tokens with the specified characteristics onto the battlefield.
If a replacement effect applies to a token being created, that effect applies before considering any continuous effects that will modify the characteristics of that token. If a replacement effect applies to a token entering the battlefield, that effect applies after considering any continuous effects that will modify the characteristics of that token.
Previously, an effect that created tokens instructed a player to “put [those tokens] onto the battlefield.” Cards that were printed with that text have received errata in the Oracle card reference so they now “create” those tokens. (CR 701.7) a 1/1 green Squirrel creature token.