ToME: the Tales of Maj'Eyal

I went into the ruined dungeon and killed everything as usual. But the last guardian suddenly... disappeared. Thinking it only used an invisibility rune/spell, I just proceeded to kill everything else in the room. And then, nothing. I waited for it to come out, but to no avail. I CAN hear it tho (it was a wolf) howling and snarling in my face. I have a feeling its trolling me hardcore. ;_;

I am having the same problem but with a goblin or orc called Aganor the Guardian who can only hit me on 9 of the tiles in the room (making me assume he is on the middle tile) but no amount of sun infusions nor chance on hit to cause damage will kill it or make it visible.

I wonder if the "unkillable" version is related to the occasional beasties -- usually summoned, I think -- that just don't die. They sit there, you can hit them all you want, and they simple...exist. They don't attack back, they don't die. If it weren't for the irritation of trying to do autosearch with them around, I wouldn't even care.