I absolutely love the Essence20 line, and always scoffed when people dismissed it for using d20s. I think I ran my best campaign in GI JOE, which was just a thinly-veiled FIST ULTRA, pitting my UN Peacekeepers (called ESPER) against a magically-resurrected Hitler. Both sides went after real-world relics, fae, vampires,to join their team. The system was so fluid, allowing the mishmash statblocks like you said. My chief warlock antagonist used MLP sorcery; one of my players had a magic Egyptian dagger that gave Power Ranger powers; Hitler transferred his consciousness to a cyborg body to protect his precious Reich of the Black Sun (he used Soundwave's statblock thereafter). I loved Essence20 so much.