Essentially Pokémon’s answer to the iconic “mimic”, the Ghost-type Gimmighoul has a Chest Form which lies in wait to surprise people and Pokémon. If they happen to open the chest, they’ll be controlled and forced to collect coins.
Mechanically, Gimmighoul’s Chest Form has the ability Rattled, so if it’s hit by a Bug, Dark, or Ghost-type move, or is affected by Intimidate, its speed raises.
As for the Pokémon’s Roaming Form, that’s a bit more of a mystery at the moment, as “not a single Trainer in Paldea has ever managed to catch one”.
It does look like that it’ll start cropping up in Pokémon GO soon, though…
Pokémon Scarlet and Violet will arrive next week on November 18th!