@Dromerd Demon going zug zug with its claws would make for a nice legendary RE, something along the lines of:
"Metamorphosis allows you to use all bear form (or cat form) abilities, and is augmented with bonus shadow damage, scaling with spell power." Maybe thinking of some synergy between warlock stuff and bear form abilities, as well as a way to get into metamorphosis quicker, like some ability reducing its CD - could be a spell caster out of demon form, and a melee dps in demon form, for an interesting playstyle.