… Maybe that statement was a little bit ambitious, but we will be adding a lot of the main ones!! This also includes grammar that isn’t slang per-se, but appears very often in slangy/manga etc scenarios.
な、わ、ぞ、ぜ、い to え sound changes, る to ん sound changes, という to つ sound changes, んじゃない/んじゃなかった after verbs for ‘shouldn’t’, etc.