There is a Necroshift skill that lets you take over the body of dead enemies, but IIRC you also take on their alignments (taking over an elite orc's body would make all orcs friendly). I remember reading it was not useful / practical for attacking, in any case.
There are statuettes that let you change shape, but the ones that can attack are much weaker than you would be normally. They can be used to attack soldiers or drive merchants out of their shops without a reputation drop, but that's about it. The frog statuette lets you move fast, even when encumbered.
