Forgotten Letter

The Forgotten Letter is a Pet summoning item that spawns a Snowy Owl to follow you around. The Snowy Owl is immune to damage from enemies and despawns upon player death. It has a 1/35 chance of being dropped by the Snowy Owl enemy in the Snow biome during Hardmode Blizzard.

Trivia

 * The item and the Snowy Owl are a reference to the series, in which owls are employed to do postal work, namely delivering letters.