I am actually hoping for a Pokémon based on this umbrella youkai since they created Mawile in Generation III.
Hmm? What was Mawile based on?
By the way, the "umbrella yokai" is called "karakasa obake" (umbrella goblin), which can also be described with the umbrella term (hah!) "tsukumogami".
Monorpale probably comes from "mono" (single, one) and "vorpale" (which is sometime used to describe a sword's sharpness)
Well, "pale" is French for sword. Vorpal, meanwhile, I'm pretty sure is a nonsense word invented by Lewis Carrol for his nonsense poem "Jabberwocky".
One, two! One, two! And through and through The vorpal blade went snicker-snack! He left it dead, and with its head He went galumphing back.
I'm french and this is the first time I've seen "pale" used for sword. Most often we say "epee" or just "lame". While "vorpale" is like you said a made-up word, it is commonly used in roleplays. "Epee vorpale" "Lame vorpale"