So the mobs can spawn with vanilla helmets (leather, chainmail, iron, gold and diamond confirmed), that can be dropped.
Also zoombies can transform into drowned and skeletons to strays, and in
/src/main/resources/data/minecraft/loot_tables/entities/
there is no loot table to replace the vanilla loot, so they can drop vanilla copper ingots and tipped arrows. not sure if those should be generated from another place
Mobs are not spawning with the supposed head armor because a tag mismatch
the tag "mob_head_armor" in: https://github.com/TerraFirmaCraft/TerraFirmaCraft/blob/0d99731dd1048126ccdd6bb49fb3fccd03a82b4d/src/main/java/net/dries007/tfc/common/TFCTags.java#L199C77-L199C77
is created as "mob_helmet_armor" in: https://github.com/TerraFirmaCraft/TerraFirmaCraft/blob/0d99731dd1048126ccdd6bb49fb3fccd03a82b4d/resources/data.py#L244
So the mobs can spawn with vanilla helmets (leather, chainmail, iron, gold and diamond confirmed), that can be dropped.
Also zoombies can transform into drowned and skeletons to strays, and in /src/main/resources/data/minecraft/loot_tables/entities/ there is no loot table to replace the vanilla loot, so they can drop vanilla copper ingots and tipped arrows. not sure if those should be generated from another place
:) cheers!