This game features a new Pokémon type called the Monster-type. There are both new and old Pokémon with this type. This is the oposite of the Fairy-type as Monster-type Pokémon tend to be scary-looking as opossed to being cute like Fairy-type Pokémon. See this page for a list of Monster-type Pokémon.
The type effectiveness of the Monster-type is:
Super effective against Poison and Psychic.
Not very effective against Steel and Fairy.
Resistant to Psychic, Bug and Dark.
Weak to Fighting, Ice and Fairy.
See this page for the Pokédex of Pokémon Heat & Cold.