Similar to Stabbity Doom's, my favorite was Beastmorph+Vivisectionist(CN), with very similar discovery choices. Preserve Organs, mummification Feral Mutagen, Vestigial Arms, Wings (maybe later I would take parasitic twin)
But the flavor of mine was different from his. Mine was an somewhat Egyptian themed Alchemist who believed he had done something that had angered the Gods and as such was trying to do everything to not die. He transformed into a Scarab with his Mutagen, as it was sacred to his people and could keep him alive in combat. He used the shield extract to harden his carapace in that state (purely fluff tbh). After being jumped by a goblin rogue he started taking preserve organs, and eventually mummified himself to try to prolong his life. The Wings were insect like (as that was one of the available options) which allowed for the scarab flavor as well as combat stuff. His endgame goal was to get the Immortality discovery, but his Mutagen self was less self serving, and might have led to him going into Master Chymist (alter ego LG).