I'm making a custom map where I use custom mobs. I want to disable the spawning of regular mobs, and have it so the only mobs allowed are my custom ones.
There's a mod called Mob Spawn Controls that may be able to help (located here!). Haven't used it in a good while though, so I can't say for sure.
Not to mention, you could do /gamerule doMobSpawning false to disable natural spawning of mobs. You will need to spawn mobs using custom spawners or command blocks.