Barging Sergeant

Mentor was built to push the player into the red zone, and this is the keyword in its most undisguised form: five mana buys a 4/2 that wants to swing the turn it lands and hand a counter to a smaller attacker it's swinging alongside. The haste matters more than the body suggests, because Mentor only triggers when the creature attacks, so a turn spent waiting is a counter forgone. Two toughness is the price for that aggression. It dies to nearly everything, but the design assumes it has already done its job: the counter lands on the declare-attackers trigger, before blockers commit, so even a chump-blocked Sergeant leaves a permanently bigger creature behind. The "lesser power" clause is the structural constraint, steering the counter onto your one- and two-drops rather than letting it pile onto a finisher, which keeps the mechanic anchored to going wide rather than tall. As a five-drop, it sits at the awkward top of that curve: the kind of card meant to extend a board that's already committed, not to start one.