Twice in the past few days I’ve come across a tower that can not be damaged.
The tower sits in the bottom right corner of the available field.
The tower also doesn’t fire.
So, while I can’t damage the tower, it also can’t damage me, but it makes it impossible to secure a 100% victory, because that tower survives any battle.
I have a player name that utilizes this invulnerable tower, but don’t want to name in forum.