We had some time ago a discussion about various ways to "freeze the mobs". By freeze, I mean make the mobs unable to hit the attacking player. I know at the moment two ways to do that.
With the first one the monster is not really frozen but maintained to a distance where it cannot hit the player. It is practiced mostly by archers with skeletons, Ladyskeletons and zombies, and also with yetis. It can also be performed with terranites and skeletons (1 tile attack range) with setzer. Agility governs this: It occurs when yout attack delay is synchronized with the monster's stunned delay, to prevent him moving. Player maintains thus the mob out of hit range.
The second one is, as Chayenne pointed it rightly, more clearly a server bug exploit. it happens under certain conditions (involving str, vit?) that I don't know exactly. If player is attacked by some mobs (I tested up to 3), if there is no loot around to be picked by looters, if there is no extra mob out of range and if there is no other player in mob's sight, a quick exit/reenter from map makes the mob unable to defend. The exit/enter can be performed either by going through a warp point or by a quisk disconnect/reconnect (change char to yourself) and attack again. It works well in 2 or 3 yetis rooms but also with other mobs in