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