Using infernalmobs-1.15.1.1.jar
on Minecraft 1.15.2

Repro steps:

Open infernalmobs.cfg and go down to the modsEnabled section.
Set several mods to false

Expected:

Disabled mods no longer appear on mobs

Observed:

Setting entries to false has no effect. Mobs still spawn with those abilities.

Workaround

To disable a mod, remove the line entirely instead of setting it to false. Note if you remove the last line in the list, make sure you also remove the comma after the last entry to avoid a JSON validation error.

Analysis

The problem appears to be in this line in InfernalMobsCore.java

mobMods.removeIf(c -> !config.getModsEnabled().containsKey(c.getSimpleName()));

This line removes any mods that don't have a key in the mobsEnabled section. It only checks whether the key exists; it does not check the true/false value of the key.

Removing the line entirely from the config file causes the key to no longer exist, which has the desired effect.

Good catch. Fixed this in commit e3c2337 and pushed Infernal Mobs 1.15.2.1 to curse