MikaDo: It might be grammatically correct, but the way you've used it doesn't really make sense. "Nobody knows why, however." is not interesting, doesn't contribute any information, and sounds awkward. You're also using "however" incorrectly here. The fact that "nobody knows why" is not really a counter point to the statement you originally made. "Nobody knows why." (without the "however") would make more sense, but that's a bit stale.
I'd suggest something more like this:
Necturine are often found in groups at the full moon. Pokemon researchers are still trying to understand why.
or
Necturine are often found in groups at the full moon. Their mysterious behavior is not yet understood.
or something else like that. See what I mean?
I do like your submission otherwise though! :)
oh and also: adjectives are descriptor words for nouns. "spiritual pokemon" : spiritual = adjective, pokemon = noun