Defend the Castle lets you send the threat as well as build the defense

Defend the Castle: Card TD gives a PvP player both sides of the tower-defense problem. The official description says you attack by releasing minions and defend against the opponent’s minions with towers. The enemy wave is also something a player sends.

That makes opposing defenses relevant to an offensive choice, alongside the tower deck protecting your own castle. The listing does not expose release costs or targeting controls, so it would be premature to prescribe when sending a particular minion is worth the expenditure.

Tower-card fusion adds a stated way to develop the defense, but no named recipe establishes a guaranteed counter. If you enjoy tower defense most when another player is posing the incoming problem, investigate the relationship between the minions you release and the towers facing them. Building your answer and choosing their question are both part of the advertised match.