Slime Boss

With this data pack, you get a fourth boss! Lord Bounce.

Lord Bounce is a giant slime, you summon him by crafting a Slime Charm. Defeating him will drop 1-9 Slime Shards.
Slime Shards can craft Compact Slime Shards and Enhanced Potions.
When you drink an Enhanced Potion, you get effects that last forever and these effects can be leveled up every time you drink the potion.
Using the Compact Slime Shards and a Slime Charm you can create the Baby Slime. When you have the Baby Slime you get a level 4 effect.

You can turn off effects and weather to use resource packs by setting their scores:
/scoreboard players set effect slimeboss 0
/scoreboard players set resource slimeboss 0