In the rich text editor:
@Styx
In a comment:
[Styx](https://chowlings.com/user/Styx)
For Names and Avatars:
In the rich text editor:
%Styx
In a comment:
[![Styx's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/Styx) [Styx](https://chowlings.com/user/Styx)