After appearing in the new loading screen background for the new year, the Lake Guardian trio of Uxie, Mesprit and Azelf finally make their debut! The trio were initially teased over the last 3 days with reports of them being sighted in the wild, the first time a legendary Pokemon has ever spawned in the wild. I think this could be a sign of things to come. Having Legendaries appear as rare spawns would be in line with how Pokemon like Suicune,Entei and Raikou would roam around the game world and were random encounters in the main series.
Niantic have also said that the Lake Trio will be available in the wild even after the event ends so if you want to get a better version of the Pokemon then keep searching. Like with Latios and Latias in their first release, the trio will be appearing in different regions. I assume the trio will then swap regions to ensure you have a chance to get each one. If not, then it will be disappointing as you’ll need to find someone to trade with or you’ll have to fly yourself out to those regions.
The trio are not exactly great or really viable for usage in raids or gym attacks so you’ll want to collect these for the Pokedex and that’s about it. For guides on how to fight each of them ,you can refer to the links below.