The book says they are immune but I remember reading somewhere they get half the effects, as compared to normal monsters not being able to move at all.

StarBurn said:

I thought that was Master monters got half the effect?

Aye. Normal monsters lose their action. Masters gets a half action. Named monsters are immune to Stun.

edderkoppen said:

+1

Master monsters have basically the same effects as heroes. Normals lose their turn completely. Named monsters just laugh at you.