I consider YabaIRyS more of an epithet than a nickname. I can't imagine anyone using it to replace her name like "I wonder what YabaIRyS (IRyS) is doing", only as a description replacing yabai like "Bruh, YabaIRyS (yabai)" in response to something she did/said.

Forgetting Faufau is pretty indefensible. It's been a long time, but that puts it in the same boat as Kronini and Sanana which I did remember.

I wasn't sure if Fuwa-chan and Moco-chan count as nicknames or if they're just how you say their names in Japanese. I guess dropping the last syllable is what makes it a nickname as opposed to just their real name + Japanese honorific?