Desu-meaning 'it is' often said at the end of sentences to seem cute or unwitting, and, Nya-a Suffix added to the end of sentences uttered by a cat/human.
Desu-Nya is a suffix that is a combination of the two. Often said(in anime) by a kawaii/loli/neko(cute/lolita/cat girl).
A descriptor used to indicate that something is a bullshit knockoff of a part of Japanese culture. Can include poorly drawn anime, weeaboos, bad cosplay, and so forth. When in reference to a person, it should be followed by 'bitch', regardless of gender. When in reference to a thing, it should be followed by 'shit'.
Originates from the DESU meme, which involves spamming forums with the word 'desu' over and over again.