Keen-Eyed Raven

A flying body that hands its counter to something already on the board, and that ordering is the whole design. The enters trigger targets another creature you control, so the Raven never keeps its own bonus: the 2/2 evasive frame stays put while the counter migrates to whatever benefits more, whether that is pushing an unblockable threat past lethal or making a small creature survive a trade. That "another target" clause is the restriction doing the work. It rules out the self-buff line that would make this a clean three-mana 3/3 flier, and instead forces the counter into the existing board state, rewarding a deck that already has a creature worth growing when the Bird lands. As a counters enabler it is modest, but the shape is precise: white has always had access to permanent +1/+1 growth stapled to small evasive creatures, and this one keeps the buff and the flier separate so both stay on the table once the trigger resolves. On an empty board the trigger has no legal target and never goes on the stack at all, which is the price of splitting the value across two bodies rather than concentrating it on one. You are paying the tempo of an extra creature to keep the counter and the evasion permanently apart, and that separation is either the point or a liability depending on what else is already down.