what's a passthrough stab? and how do I do it?

[Jimjam]

When a mob begins it's attack or cast animations it's facing is stuck until the attack is complete.

As such, you can move in such a way to be facing the mob's rear in order to backstab the mob.

One way to do it is to move behind the mob, let it attack you, then quickly step back and backstab as it is swinging.

Another way is to face diagonally while fighting the mob, then strafe into it's rear and backstab as it swings.