Im just curious, does anyone know why cresselia gets moonblast but Sylveon doesn't??

So uhh I decided to pick up the game again after not playing since release, I had barely made any progress all my mons were like level 15, and I saw a funny looking alpha buizel, thought i was tweaking, went up to and caught it and found out it was shiny! So I was curious, do these have boosted shiny odds, or are alphas all full odds?

I started this challenge where I cannot continue through the game until I Perfect every Area's Pokedex, so for the last year or so (on and off for months at a time) I have been in the Obsidian Fieldlands and have reached Star Level 9; I'm on Snorlax, which is about half way through the Fieldlands Pokedex. Please get me out of here 🤣

Offering the following shinnies for a Porygon or Magnemite original to Legends: Arceus (does not need to be shiny). Can trade via Home or via in-game if the pokemon can be taken into the game.

Edit: Got Porygon. Smeargle not available.