In the rich text editor:
@Oxytail
In a comment:
[Oxytail](https://cometcrashers.org/user/Oxytail)
For Names and Avatars:
In the rich text editor:
%Oxytail
In a comment:
[](https://cometcrashers.org/user/Oxytail) [Oxytail](https://cometcrashers.org/user/Oxytail)