I thought this had better reminder text before--I don't like seeing "resolves" on a common, even in reminder text

Using "resolves" lets you print it on cards that don't target creatures, and lets you cast those without there being a creature on the battlefield.

Sure, but it still adds a complicated term. But that said, "resolves" does appear in the reminder text for rebound and buyback.

If you wanted, you could give it two different versions, like Wizards did with Haunt: compare Cry of Contrition and Blind Hunter. That's generally the most sensible way to go with keyword abilities that work on both spells and permanents.

this keyword does have two different versions. This is the version that goes on non-permanents, there's an etb trigger for the one that goes on permanents.

Really? A triggered ability on a sorcery? Also, there's absolutely no reason not to just have the text be "Put two +1/+1 counters on target creature." I think this would also work fine as a 2G instant.

Went back to old wording with "You may ... on up to one target creatures". It's janky, but I guess it does what you expect most when you expect it to happen.

Gather Courage got removed, so this is now an instant again.