Choose one: Pay 4 Force Retreat an attacking unit. Its attack ends. (It is considered to have attacked.) Play only if the defending unit's remaining health is higher than the attacking unit's remaining health.
Or: Pay 6 Force Choose one of your opponent's units. Tap that unit and move it into the build zone. Play only if you have a unit in the same arena with higher remaining health than the chosen unit.
You may activate one or the other effect, not both.