Master Mode

Master mode is an option that can be selected during world creation. It further increases the difficulty of the game beyond Expert mode (3× the difficulty of normal mode), offering Master mode-exclusive items. Like Expert mode, Master mode begins the moment the Master mode world is created, and cannot be altered after that by the player.

General
All enemies and bosses have their health increased by 50%. For example, the Blue Slime has 75 health instead of 50 and the Wall of Flesh has 16800 health instead of 11200. This buff is applied to the Expert mode health value.

Bosses
Bosses in Master mode drop a "relic", a statue resembling the boss. They also drop a pet-summoning item which summons a pet that either resembles the boss or is closely themed after it.

Items
While not known, Bosses may drop "Master Mode" exclusive items similar to Expert Mode Exclusive drops

Player
Players gain an additional accessory slot that is only active while in a Master mode world. This stacks with using the Demon Heart, meaning the maximum attainable accessory slots is now 7.

Trivia
Master mode's descriptive text "Game over man, game over!", is a quote from the 1986 American science fiction action film Aliens.