Whenever Bucky Barnes attacks, he gets +1/+0 until end of turn.

When Bucky Barnes is dealt 5 or more damage in a single turn, prevent that damage and transform him.

Menace

As long as an opponent controls a creature, The Winter Soldier is an assassin in addition to its other types.

Whenever a creature deals combat damage to The Winter Soldier, put a -1/-1 counter on that creature.

{T}: Destroy target tapped creature.