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
Players will drop 100% of their Coins upon death instead of 75% in Expert mode and 50% in Normal mode.

In master mode, store bought items cost 25%-50% more in comparison to the other modes. In addition to this, selling items only yields 83.33% of the original value in comparison to the other modes.

Enemies
All enemies are stronger, therefore it's harder than expert mode.

All enemies have their health increased by 50%. For example, the Blue Slime has 75 health instead of 50.

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

Bosses have their health increased, listed in the table below:

Items
Bosses drop "Master Mode" exclusive items similar to Expert Mode, but they also drop their treasure bag, which contains the expert mode items of the boss. They have a 100% to give a Relic of themselves, and a 25% chance of giving a pet, also modeled after themselves.

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

If in softcore mode, upon death, the player will lose all of their coins instead of 75% in Expert mode.

Trivia

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