my friend keeps using malekith against my TG slann and i cant kill him so i cant move my TG as he kills like 1 or 2 a turn
Malekith is not unbreakable, he is only immune to psychology. His special rule about autopassing tests applies only to panic tests, not break tests. That being the case, you should be able to win through combat resolution and break him. Just make sure he doesn't fight anyone with wizard levels or magic items since he is able to remove the item/level on a 4+ if he hits in CC. Simply buff your TG with life or light. If he is only killing 1-2/turn, you should be winning by 3 or more which means he is breaking on a 7 or even higher.
Panic (pg. 62) and break (pg. 54) tests are distinct and different tests although both are leadership based. Under Malekith's rules, any druchii unit within 12" autopasses any PANIC test. Since the rules don't stipulate otherwise this would even include a panic test induced by Malekith breaking within 6" of them!!