Ah, there would be that block, good. Means I don't have to worry about blocking it to avoid spinlocks or anything. Well, unless they decide to make the Ring of Carcer non-Permanent.
The way it is coded, even once the Ring is removed, the Tile will remain locked to units under level 15.
I'm invincible!
Or one that keeps powerful enemies at bay killing the caster in the process:Well, the level block isn't actually tied to the improvement, but is handled in python. It wouldn't be hard to create a spell that keeps weaker units at bay.
Actually, that could be an awesome Force spell. It could block set a level prerq for the tile equal to the caster's level. It would probably have to immobilize the caster too, and only be a temporary effect.