Breeder Rank: B
Monster Rank: D (but much higher is recommended)
Location: Angwass Road in months 3-5 (Spring) only

I highly recommend you do this with a Rank A or better monster.

Cross both bridges and head toward the cabin at the end of the road. An event crystal will be there. you will be attacked by a wild Joker. The joker is quite strong. Defeat the joker to get the combining item and unlock Joker.