A “repulsion” intrinsic. This prevents monsters that fail a resistance check from moving next to you (specifically, where they believe is next to you) on their turn by making their AI consider it an invalid position. However, if you are in melee range, it does not make them step away from you or refuse to fight you, nor does it prevent them from making ranged attacks.

This intrinsic could come from some new artifact or spell, but two possible sources for it that already exist are reading the scroll of scare monster and casting the spell of cause fear.