This mod allows you to increase your game difficulty with the following:
The list of spawn variants is as follows:
Creeper → Charged Creeper
Zombie → Husk
Husk → Zombie
Skeleton → Bogged
Skeleton → Stray
Skeleton → Parched
Bogged → Skeleton
Bogged → Stray
Bogged → Parched
Stray → Skeleton
Stray → Bogged
Stray → Parched
Parched → Skeleton
Parched → Bogged
Parched → Stray
Spider → Cave Spider
Cave Spider → Spider
Blaze → Breeze
Breeze → Blaze

The mod is fully server-side and works on single-player worlds. It will not alter any data on your world and can be installed and removed as you need.
Unlike other similar mods, this will not add minor bugs such as enemies dropping equipment in the Trial chambers or not applying potion effects in a one-shot kill.

You will find the config files under config/ultimate_monsters (new folder).
config.json allows you to tweak the chances of every monster to spawn altered (variant). 1 means 100% of the time, 0.5 means 50% etc.permanent_effects.json allows you to apply effects to the mob. These last forever and cannot be removed from the mob.damage_effects.json allows you to add effects to the entity hurt by the mob.

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