InControl, while powerful, has a few issues. It often doesn't respect mob cap rules, spawning mobs non stop until the game crashes, and it also is a little more difficult to set up. Overall it can lead to performance hits if doing large numbers of spawns.
Instead of using inControl's potentialspawn.json to add a mob spawn, you can instead use BiomeTweaker. BT has the benefit of respecting mob caps by default, and is a little less buggy. The allow and deny checks that you have for inControl will work the same way regardless of which mod adds the initial spawn, so if you already are using inControl, the switch is actually very simple (I'll add the inControl methods too for those that are unfamiliar with it and looking to set up the system from scratch. Switching to BT means you need to delete any spawns in potentialspawn.json for which you are moving over. Pretty much any non specialized spawns that can use a biome as a target can be moved).
#Efficient custom mob spawning
urban kernel
For BiomeTweaker, you just need to add this to your script file:
yourBiome.addSpawn("MOD:MOB", "TYPE", weight, groupMin, groupMax)
One of these entries for each mob you want to add a spawn for. BT does one thing different in thatt it specifies by biome, so instead of using inControl rules in your spawn.json that allows or denies based on biome, you pick biome in your BT script.
I'm not going to cover what all the values mean since you can reference the BiomeTweaker wiki, but I will mention that mob spawn weights in Minecraft work as a chance system that is measured against every other weight. E.g if you set every mob's weight to 5, you wouldn't get mobs spawning less often, you would just give them all an equal chance to spawn. For reference, endermen have a weight of 5 and zombies a weight of 100.