Juvenile version of New England adjective "Pissah" when your mother wouldn't let you say bad words. Means "great" or "awesome". Derived from "pissah" and "whiz" in use by children.
This candy is wicked nizzah.
Nizzah is another way of saying "niggah". It's a more acceptable way of white people (e.g. Jailbreak players on CSS) to say it. It's also a way around the no racism rules.
You: Fuck you, nigger.
Me: WOAH, WOAH. NIZZAH PLEASE. I DON'T NEED THAT LANGUAGE.