I really love supreme incarnation as a class chassis capstone. It's fluffy and unique. Narratively, I love a party of adventurers that have traveled together for 19 levels with one of these weirdos constantly talking about the "spirits" they talk to while they do their magic schtick. Some of the party members might roll their eyes but come the end of the game they incarnate when the animist casts avatar and the nonbelievers scream "my gawds, they were real the whole time!" I'm just picturing the kid version of Hailey Joel Osment transforming into Bruce Willis!