@HipsterFilter

They have no Rarity since they are the 2nd stage Evolution from Shileo (who is Rare)

So if anything, you can consider them Rare since the base form Shileo is as well

Still a cool looking pet, happy Jade Orb farming for the needed evobar!

Hey there @HipsterFilter, welcome to the game!

As Yubelchen said, Shiroking can be acquired by evolving Shileo twice. To find Shileo, you'll need either a red or gray pet, and some luck (and/or eventually rarity excluder potions, when you have enough resources to make them).

As to whether or not Shiroking is legendary, officially it's not, but I'd certainly consider it an endgame pet because of how many resources are required to make its evobar.

I hope that answers your question; let us know if there's anything else we can help with ^^