TerrariaChatRelay is basically just another chat bridge plugin between the terraria chat and a discord channel(s), of which you might’ve seen something similar on T1 or other servers. It is essentially what Phase is to DG, but on discord.
I once got the idea of suggesting its use on DG after using it on a personal server but in some “relatively recent update” for it, support for the main feature I had in mind has seemingly been removed due to abuse(unsure about that), being that you could edit formatted messages in its config to ping roles/people. That briefly came up in https://forum.dark-gaming.com/t/discord-role-that-pings-players-when-a-boss-is-summoned/8198/14, but is obviously a dead thought now if support for it has been removed.