The most USELESS monster.

1) Regarding the plague: The plague does not affect demons because they are creatures of Death. 2) Fairies and demons are completely different units and are needed for completely different tasks. Demons speed up the hero and steal mana. Fairies block ranged units and can inflict targeted "bites" (since they are weak, they are not always immediately attacked, and due to their retaliatory attacks, they can also damage units). Fairies also speed up the hero; this is their only similarity. 3) Dwarves are certainly strong, but they are practically useless in the final battle because they reduce the army's mobility on the map, cannot withstand strong attacks from troops that are not of the first level, and also require money to hire, and even if it's not a huge amount, it's still enough to make you think twice about spending it. 4) Leprechauns are an excellent monster; summoning one in battle is great, and it's free luck! And that's all you need. 5) Skeletons are slow, but you can gather a lot of them, and they provide good protection against ranged units. 6) Trogdolites are probably the most useless unit; they don't offer much benefit, and they are not always available. That's just my opinion, for the sake of discussion