I think it might be related to where I gave Duriel Spin to Win. SK1 is used for closing distances, and the animation was his charge (using A1 and A2 appears to bug him out, since his AI is based on whether or not to use those anims if I recall.)
I noticed in general that if you don't give an AI the right skill, the either refuse to use it, kill themselves immediately when using it, ooooor that

btw. you can change dark summoning missile func from 39 to 6 to summon a specific monster, much easier for testing stuff

Thank you, was trying to remember how to do it. Where do I define how to summon the monster though, in par 1 of the skill?