Actually as I understand it, is 1-10, 15, 20, 30, 40, 50, etc so basically once you10 its once every 5 leves then once you hit 20 its once every ten level ups. I'm not yet to 25 so I can't confirm this but thats what I recall hearing from one of the GMs a long time ago.
Supposedly your level affects your chance of getting good rares, so in theory your level up at 15, 20, and so on should have more high rarity cards to choose from then your 1-10 had, and supposed once you hit the really high levels your all but guaranteed 4 or even 5 star rarity cards.
This again I was told by a GM, I haven't found it to be the case as not only 1-10, but 15 and 20 have been 2 star rarity cards for me -_- but I have heard people say they got 3 star rarities for their 10, 15, and 20th so I may have just been unlucky.
The bunnies of Lavato have special abilities, like 'Action Skill: Make Carrot Disappear.'