Whoops. Slakoth can't be shiny. The others can. Can send through an Uxie if that happens. Some people are claiming to have heard the Trio will rotate, while other sources say they won't. At some point, Niantic will open it up:
Feebas Day (shiny): People got mad because they didn't get a shiny Feebas, and Feebas came out in eggs and raids.
Clamperl Day (shiny): People got mad because they didn't get a shiny Clamperl, and now it's in raids (and had better odds and smoother quests on the Day.)
Regionals: Popped up in eggs all over the world.
They will rotate them at some point, or open them up in one way or another, for a short period of time.
I actually really like seeing the different stops around the world. Most are fairly average, but you sometimes find some amusing stops.
Community Day, evolved my 96% I had saved, and nothing higher than that spawned in our area. In the city, reports of 2x 100%'s in the same park. I got a good number of shinies, 7 or 8 I think. I was working more for stardust - I purposely finished off the rest of my dust so that I only had a few thousand, and ended the day with just over 100,000 dust. I burnt out part way through, but it was interesting checking out the new lure mechanics. Some people dropped those in the area.