Niantic confirms Pokémon GO players who receive an EX Raid invite will get a chance to encounter Deoxys Attack Forme after today, December 20

Niantic has confirmed that Attack Forme Deoxys will soon be available in Pokémon GO EX Raids for the first time. 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 Attack Forme Deoxys. According to Niantic, battling Attack Forme Deoxys is 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. 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. Niantic has also confirmed that Trainers who will receive an EX Invite after December 20 will get a chance to encounter Deoxys Attack Forme.

Source: Niantic Support @NianticSupport