Niantic has confirmed that Defense Forme Deoxys is now available in Pokémon GO EX Raids for the first time. The DNA Pokémon appears in EX Raids with stronger defenses than previously seen, so make sure your team is prepared. Pokémon GO EX Raid invites to battle Defense Forme Deoxys are now being sent out for to eligible players. You can become eligible to receive an EX Raid Pass when you win a Raid Battle at a qualifying Gym. You’ll be able to see which Gyms can host an EX Raid through a handy tag when you look at the Gym details.
EX Raid Passes will give you the date and time when you’ll be able to challenge Defense Forme Deoxys. Battling Defense Forme Deoxys will be a difficult challenge that requires Trainers to take advantage of every opportunity—so don’t forget to invite a friend to go along with you! Remember: invites can only be sent to an Ultra Friend or Best Friend, so don’t forget to battle with friends, send Gifts and trade Pokémon to build up your Friendship level.
Source: Official Pokémon GO blog and @PokemonGoApp