If there is X copies of the boss in PVE active and someone tries to spawn another one then it should get blocked because you can hit enemy cap with only one boss and then no one could fight elsewhere.
Here are the proposed limits
- King slime - 30
- Eye of Cthulhu - 30
- Eater of Worlds - 3 (due to its segments)
- Brain of Cthulhu - 5 (due to its creepers)
- Queen Bee - 25
- Skeletron - 15
- Deerclops - 15 (if it gets implemented in PVE)
- Wall of Flesh - 1
- Queen Slime - 20
- Destroyer - 1 (due to segments and probes if it gets unblocked)
- Twins - 10
- Skeletron Prime - 8
- Plantera - 8
- Duke Fishron - 10
- Empress of Light - 1
- Golem - 15
- Lunatic Cultist - 7
- Moon Lord - 1