The Oath Forest is a small area to the north of Floccesy Town and doesn't offer much. At the top is a massive stone which Keldeo will interact with

Keldeo Event
If you bring the event Pokémon Keldeo, you'll be able to teach your Keldeo a special move which will also change its form to the Resolution Form.

Name	Type	Cat.	PP	Att.	Acc.	Effect
Secret Sword			10	85	100	It slashes at the opponent with its long horn. The mysterious power of the horn deals physical damage.