As of this week, Groudon is no longer available in Pokémon Go in the UK. Instead the god of water, Kyogre, has started spawning in gym raids across the country. Kyogre will only be around until the middle of February, and is one tough cookie, so if you're lucky enough to spot a raid then here are some tips for defeating and capturing one.
First up, while the raid has a recommended team size of 20 players, a bit of experimentation suggests that as few as five can take down the behemoth. (You'll need five decent players, and it may be a bit close to the line on time.) As always, local Pokémon Go raid Facebook groups seem to be the easiest way to organise a team for a particular raid instance.
Regarding team selection, you're going to want as many sturdy and heavy hitting electric type Pokémon as possible in your party. Raikou and Zapdos are both smart choices in that their high HP and strong attack stats mean their electric attacks should do easy damage. Any sturdy grass types also work well, particularly ones with solar beam, and even Groudon with Solarbeam can work in a pinch to deal some last minute large scale grass damage.
When it comes to catching a defeated Kyogre, the water whale is abnormally wide, meaning the game sets it quite far into the background to show it all at once. Because of this, hitting it with excellent hits can be tough. If you have access to AR+ as an up-to-date iPhone user, you may find it easier to hit if you very carefully close some of that huge distance. The catch rate for Kyogre seems pretty low, so be prepared to tackle the raid more than once.
Good luck, and may your raid be legendary.