In the rich text editor:
@Heavenly_Mistakes
In a comment:
[Heavenly_Mistakes](https://chowlings.com/user/Heavenly_Mistakes)
For Names and Avatars:
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%Heavenly_Mistakes
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[](https://chowlings.com/user/Heavenly_Mistakes) [Heavenly_Mistakes](https://chowlings.com/user/Heavenly_Mistakes)