I still have no idea why I’m trying to make myself feel that festivals have no significance to me but I have maths tuition starting from 2pm and it’s almost noon now so I’ll go home and grab a bite

wait a second

As from the files you find in the game, Cosmog is forced to use its special ability to make Ultra Wormholes appear through immense pressure.

But what exactly is the pressure applied?

From the cutscene, Cosmog’s power looks like this: 

(Source: Pokeli’s Pokemon SuMo cutscene collection)

Seem familiar? Look at the animation for evolution:

(Source: Prof.NoGood’s “How to evolve crabrawler”)

And we do have a previous encounter on forced evolutions!

(Source: PurpleRodri’s HeartGold playthrough: Episode 15)

Tl;dr: Cosmog is forced to evolve and the energy exerted is used to open Ultra Wormholes

Anyway since I have to tucker down to start revising my Pokemon Moon run won’t have its first champion defense battle yet

It’s exactly like my AS run which is still just after the Kyogre part