>>25021713All of them could possibly come from plants I think, except Ghetsis.
From Bulbapedia:
From "G" and "Cis" (C), the pitches of the timpanis used in his battle theme. The combination of "G" and "Cis" is a tritone, previously referred to as Diabolus in Musica (The Devil in the Music) in the 18th century. Could also be romanized as Goetis, derived from Goetia, Greek for "sorcery".
Last part of that I'm not sure, but the G C# part was stated by Masuda himself.
