Ment
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All the issues stem from the fact that the game considers that 2x2 square to be the creature itself. I initially thought that, for example, you could only attack a creature by targeting that square, until I tested it.
Let it be a boss in some kind of dungeon, with a battle triggered by a script. With a rare chance of appearance, like an Easter egg boss. Remove the possibility of it appearing on the map. Most of the problems will disappear immediately.