Forge version: forge-1.7.10-10.13.4.1558-1.7.10-installer
Twilight Forest version: twilightforest-1.7.10-2.3.7
Link to crash log: no crash

Steps to reproduce:
1.

What I expected to happen: I expected that I would have to fight mobs before defeating the boss
What happened instead: No mobs before boss, only the boss spawns

For the green snake boss (the Naga), that is intentional, aswell as the Hydra in the fire swamp.

i know that but like only the bosses spawn with every dungeon except if there are spawners

1.7.10 is not supported.