For those who may have recently re-joined Pokémon GO or those who just have not been able to achieve that golden prize of an EX Raid Pass, here is some information you might find useful!
What is an EX Raid?
An EX Raid is an invitation-only Raid in which an exclusive Pokémon is the Raid Boss. In the past, it has featured Mewtwo and various form forms of Deoxys.
This is the only way to obtain Deoxys in Pokémon GO. You must have an EX Raid Pass to be able to join an EX Raid, or be invited by an Ultra (or Best) Friend to an EX Raid.
How do I get an EX Raid Pass?
You must a) raid at an EX-eligible gym, and b) that gym must be triggered within the (weekly) cycle you did the raid in. Even with both, there is no guarantee of a pass, so some persistence is required. In central London, this amounts to targeting known past EX gyms. More locally, enquire with your local group; you may have to trigger a Gym yourselves.
Having done a single Raid at a triggered Gym is sufficient and nothing else is known for certain to increase your chance of a Pass (except covering multiple Gyms, of course).
The other option is for an Ultra (or Best) friend to invite you to the EX Raid. Trainers who receive an EX Raid invite can send this to one Ultra (or Best) friend. If that person declines, it cannot be sent to another.
How do I invite a friend/get invited to an EX Raid?
If you recieve an EX Pass, there is a link to "Invite" a friend. This will bring up a list of Ultra (or Best) friends you can invite. We suggest that you only send an invite to someone who can definitely join, as you cannot send it to multiple people or to another person if your original invitee cannot attend. The recipient will see the invite pop up in their game and it will appear in their items.
Which Gyms do you mean? Do you have lists, maps, stats?
Have a look at this page (on desktop). It contains (linked separately for mobile):
How can we trigger an EX Raid?
In central London, there is high activity so Gyms are often triggered and you can just Raid some. Locally, once you've found an EX-eligible Gym, try to achieve constant activity on that Gym with around 30 unique Trainers within a single weekly cycle (between when Passes are issued). Although this method is not foolproof, it has proven successful many times. With the new update, EX-eligible gyms are marked as such in-game in the top right corner of the gym screen "EX RAID GYM".
Previously a gym could not be triggered for an EX Raid in consecutive weeks and a gym that gave out EX Passes would not have any raids until the EX Raid completed. This is not currently the case but it is not known whether this means that a gym can have EX Raids on consecutive weeks.
I/my local group followed all of the above info but I/we did not successfully trigger an EX Raid/get a Pass; why?
When are EX Raid Passes distributed?
EX Raid Passes are distributed in waves every 7 or 8 days, exactly 2 days before the previous week's EX Raids are due to happen (sometimes, there's a random wave not fitting this pattern). Whether it's 7 or 8 days alternates, meaning the day of the week of the EX Raid increases approximately fortnightly. Passes are usually distributed at around 7pm. If you want to see the history of Pass distribution dates, check this table.
Note that this frequency may change with the Deoxys cycles but this is not known for sure. We will update this guide as we gather evidence.
Does having a silver/gold Gym Badge increase my chance of getting an EX Raid Pass?
Niantic have said that yes, it does. They announced this after their reform of the EX Raid system. However, they had previously announced the same thing, only to have it refuted by a statistical study on The Silph Road, which showed a weak opposite correlation. As such, it does increase your chance if you believe them, but it shouldn't stop you from trying at lower badge levels either way.
After getting one EX pass, does my likelihood of getting another decrease significantly?
No. Even anecdotally, people tend to have no problem accumulating EX passes. Keep trying to get a 100% IV one by doing some more raids!
I can't go to my EX Raid; what can I do?
If you're comfortable sharing your login details, you can ask someone else to use your account and attend for you. You can seek people willing/able to do this for you in the private channel set-up for your Raid, or in the general #ex-raid-chat channel, both on the Pokémon GO London Discord. Alternatively, you can try contacting Niantic (pokemon-go-support@nianticlabs.com) to beg for compensatory Raid Passes or such.
If you invite a friend to attend an EX Raid and you cannot join, it is not known whether they will be able to do the Raid.