Pathfinder, D&D, Cyberpunk, etc.
I'll post what started this idea. My current character, the half-elf rogue Irini. She was a backup character I made after my original was knocked out and taken by Demons during the Path of the Righteous campaign. I had originally planned to bring her back to the Capital once we have rescued my initial PC, but I started to have more fun with her than I did with Utrop.
I built her solely for DPS. Maxed out her DEX and replaced the racial feat Adaptability for Ancestral Arms to allow her to wield the Elven Curved Blade: Which was a two-handed weapon that can also be used with Weapon Finesse to take advantage of the DEX boost. And mostly used the rogue talents to gain combat feats that may suit her during fights.
But for some reason, my GM turned her into a slime girl an ooze lord. Highly acidic, too. As any non-magical item she had were dissolved instantly. And even better were two especially lucky rolls of a 1d100, that she somehow gained the spell dimension door and can summon forth a pair of slimy wings that resemble that a luna moth's in terms of silhouette.
As of now, she has adopted another slime person a tar child. This happened during the fight with the Herald of the Ivory Tower. Turned out the final bout was taking place above a mythic colossal tar jelly. Said jelly grabbed Irini and tried to absorb her, but also being an ooze type allowed her to convince the jelly to grab the herald and assist us into absolving him.
Turns out the jelly was an amalgamation of all the prior adventurers that tried to take on the Herald before us and failed. After making the GM laugh that this thing was my child, he allowed me to coax the jelly into humanizing a tiny portion of it into a personality. It would only cost him a tier of his mythic level to do so and now I have bardic cohort that plays buffs on a haunted hurdy gurdy.
I have plenty others. But I'll delay to see if anyone is brave to post here their experience.