So can a unit of temple guard with a Slann get stomped on of any kind? Or does the unit benefit from the mixed unit amunity. The Slann has a monsterous base.
Base size doesn't factor in to what type of unit a model is. The Slann is classed as infantry, and so gains no immunity to things like killing blow, stomp, etc. With that said, it's actually a good thing that he's infantry- otherwise he wouldn't get Look Out Sir against templates and such.