Darumaka evolves into Darmanition at level 35.
Darmanition will get the Zen Mode Ability only after you have defeated the Elite Four, capture the exclusive Legendary in your game which is either Zekrom or Reshiram, and then defeated N and Ghetsis, and then receive the National Pokedex. Once that's done, go to the Relic Castle where the statues are at and approach the entrance. Juniper will be there and she'll give you a RageCandyBar. Interact with any of the statues and it'll activate a battle with Darmanitan. Those statues are all Darmanitan and they all have the Zen Mode Ability.