To mention a role or user use the numeric ID instead of the display name.
Using developer mode User settings -> Appearance -> Developer Mode -> enable and now you can find id of any user, message, channel or server with right click -> copy ID

Using developer mode User settings -> Appearance -> Developer Mode -> enable and now you can find id of any user, message, channel or server with right click -> copy ID

Updated on: 12 / 12 / 2018