Scarlet [Boss Name]
If you were to modify with the game's files in a certain way, a boss will spawn about a day and a half later, and it will resemble a red,
larger version of the latest boss you defeated. It will have the ability to speak, will taunt you, and will act like a buffed up version of said boss. If you fail
to defeat it within 42 in-game hours, it would delete the game, and you have to re-download it fresh to play Terraria again.
Bestiary entry: "An entity created from the messing of the cosmic code, and can change form depending on whom it fights. Its reality warping abilities allow it to delete the messed-up file should it remain undefeated for long enough".
... Technically this actually was from a Minecraft-related dream and involved the Scarlet Wither (who was just a buffed Wither Boss who could speak and was red). However I cannot see why there can't be a Terraria (joke) equivalent.