"Donphin Oni" is rankable as it could be seen as an alternate way of typing "Dolphin's Oni"
This is a marathon map with multiple difficulties so i guess this rule does not apply
And Donphin is totally related to your name as i said.
see the "unrelated to an username" part of it as well as the "Marathon maps with a single difficulty may use free naming"
I'm unsure about the part where different gamemodes come in since it's not explicitly stated anywhere
I think our best bet is to ask a BAT at this point.
Taiko diffs and Standard diffs can be separated and recognize as two individual "mapsets" so right now we have two single diff spreads in a single set.