Secret world seeds - Official Terraria Wiki

Secret world seeds are world seeds which have been discovered as secret easter eggs that generate worlds with strange or unique features. Unlike regular world seeds – which only affect the usual world structure – secret seeds can produce worlds with characteristics that would not be attainable through normal world generation (i.e., they can affect the game's mechanics while playing in that world). For instance, they may change enemy statistics and behavior, item drops, graphics, theme music, and more.

Working as Designed - World Generation for Secret Seeds

Secret world seeds - Terraria Wiki

Remix Secret World Seed Guide for Terraria 1.4.4 - KeenGamer

Secret world seeds - Official Terraria Wiki

Secret World Seeds - The Official Terraria Wiki, PDF, Wiki

Ethera - The Divine Dimension [V1.1.0] [OPTIFINE] Minecraft Data Pack

Best secret world seeds for Terraria 1.4

1.4.4 - Official Terraria Wiki

Secret World Seeds - The Official Terraria Wiki, PDF, Wiki

Every NEW SECRET Seed in Terraria 1.4.4 Labor of Love

Secret seeds now have unique icons in the World Select menu! : r/Terraria

Secret world seeds - Official Terraria Wiki