Invisible Name Characters

Hello,
I know there are some characters that you can use in your summoner name but are invisible in client chat, champ select, friends list, etc.
I cannot find characters that are not blocked when creating your summoner name. Chinese characters are not allowed, alt codes aren't.

I know there are still characters that you can slip in there. What are they?

u cant add Special characters, that was a long time ago.. now u cant!