Definition:

Master mode is the hardest challenge I've ever made to a pokémon fan. It can be done in every game but requires modifications or cheats to actually work due to some rules.

It consists of taking the game to the extreme and ripping off mechanics or whatever would make the game easier for the player.

It is recommended to play this in Pokémon Radical Red in hardcore mode to take it to the extreme.

Rules

Permadeath rule: If any pokémon the player has is fainted, they die and cannot be used anymore. You can either store it in your box (recommended) or release it. If all of your pokémon are dead, you must delete your save file.

No EXP rule: The player must not get EXP from winning any battle. The player still can use items that level them up, and they will work, but these are the only ways to Level-up.

No Pokémart rule: You cannot buy in the Pokémart.

Move force rule: When you are given a TM by a gym leader, you must forget the move you most used in the battle in the pokémon you used for most turns in the battle and learn that TM in its place.

No healing attacks rule: You cannot use healing attacks.

Worthy trainer rule: You can only catch one pokémon per Gym badge you have. This does not count for static encounters (all gift pokémon are considered static encounters by this rule).

One use pokécenter rule: You can only heal once total in pokécenters per Gym badge you have. After healing in a pokécenter, you cannot heal there again until the challenge ends.

First pokémon rule: You must catch the first pokémon you find in every area. This only counts after you already got your first pokéballs.

No trading rule: You cannot trade pokémon, except for in-game trades.

Ending rule: This challenge ends when you beat your region's champion.

Losing rule: If all of your pokémon die, you must delete your save.