Mercenary is a piece that transforms into opponent's once it takes an opponent's champion and saps the opponent's morale.
Strength: The level one Mercenary is the cheapest Minion able to move and attack in a plus formation. Mercenary is able to take a champion, sap opponent's morale, and prevent itself from being taken since it is now the opponent's piece. At higher levels, its amount of pressure is very high on minions, since it will remain on the attacker's side even after taking a minion.
Weakness: Mercenary could attack your champions once it becomes your opponent's piece. Higher levels of Mercenary are more powerful, but are also costly and thus have trouble trading with other minions. It also has diagonal weakness at all levels.