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?
I’d move Goomba up a tier, but other than that it’s pretty good.
Funny how even among the top tier there’s a big gap imo: you’re sometimes reminded of Ina’s full name by “Mama’nis” and “Ane’nis” existing, plus she (rarely) introduces herself with it. “Baelz” is “Subaru is the manager of an esports club”-level of forgotten lore.