You can poison any Loomian regardless of their type. Your Fire-type moves have a small chance to poison the target.

Smoal	Fire Toxic	ForgeScorching Skin	Blistering Heat	HP 37	En 67	AtkM 38	DefM 30	AtkR 38	DefR 25	Sp 54
Charklin	Fire Toxic	ForgeScorching Skin	Blistering Heat	HP 56	En 77	AtkM 74	DefM 52	AtkR 74	DefR 39	Sp 84
Billoforge	Fire Toxic	ForgeScorching Skin	Blistering Heat	HP 80	En 87	AtkM 112	DefM 104	AtkR 112	DefR 61	Sp 24