Belligerent Yearling

A two-mana beater whose ability does nothing on its own until another Dinosaur enters afterward, and only starts paying off once you chain more Dinosaurs onto the board. The power-copy is a base-power set, not a buff, so it overwrites rather than stacks, and it resets at end of turn: each subsequent Dinosaur re-triggers the option to match that creature's power until end of turn. The timing is the whole story, and it cuts against the trick-shaped reading the effect first suggests. Because the trigger fires on another Dinosaur entering, and most Dinosaurs come down at sorcery speed in a main phase, the upsizing almost always happens before you attack, in full view of the opponent, who then blocks the newly enlarged body accordingly. This is not a combat ambush; it is a threat you telegraph and hope goes unanswered, with trample making the extra size matter when they block small. The "you may" clause is doing quiet work: since the effect sets base power to the incoming creature's power outright, you decline it whenever the new Dinosaur is smaller than three, so the option guards the floor rather than forcing a downgrade. It is a tribal reward built as a tempo lever instead of a lord, asking you to sequence your fattest Dinosaurs after this is already on the field, and rewarding a curve that keeps adding bodies over a single haymaker.