Following on from yesterday's addition to Pokémon GO, today a new trailer was released which confirms the Pokémon to be Gimmighoul. It is Ghost type and has two forms - Roaming Form, which is the one appearing in GO - and Chest Form, where it tries to get people to give it coins.
The Pokémon GO website also added an update, confirming that linking Scarlet/Violet with GO will allow catching the Roaming Form in GO, which can then be transferred (via HOME) to SV.