Relaxed Mode is a mode in Dicey Dungeons introduced in version 2.0 with the Reunion update. It can be accessed by going to the Options menu, selecting Gameplay, and then enabling Relaxed mode. When this mode is active, all enemies will have 25% less health, leaving them with 75% of their health (rounded down).
The only exceptions to this are the puzzle episodes: enemies in the Witch: Halloween Special will keep their normal health values and Madison during the Witch: Reunion episode will still have 200 health.
The 25% health reduction (and rounding down) is applied before the health increase caused by the Elimination Round and Parallel Universe episodes as well as any health increases caused by the Vacuum or Drake Bonus Round rules. This means that the Pirate will have ⌊(⌊26*.75⌋*1.1)⌋ = ⌊19*1.1⌋ = 20 health during the Elimination Round episodes with Relaxed Mode active, instead of 21 health.
Relaxed mode can be turned on and off at will, unless you are in the middle of a battle.