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It is definitely too powerful. You don't want to be putting territorial class, or win the battle in it. Silver has lplenty of that already. Just something to throw in your deck if you happen to get initiative. Perhaps interrupt the fortress, then place it on the fortress to negate it for 5 turns, then discard that enhancement to discard the fortress. So that your opponent cant somehow recur it for 5 turns, but give them some time to figure out a way to get rid of it. I think that the cards Cactus has been making are just too strong. They need to make some cards that actually focus on the main purpose of the actual card instead of just saying "Do this this and this AND win the battle..." Its as if having the right cards is more important than the skill of the player that actually uses them..