So I tought ,isn’t it obvious why Niantic skipped this little generous dude?When i first saw that he was missing I instantly tought about a Christmas event,and,this is what I was able to come up with:

As you can see,Delibird’s special feature is sharing(I made this so he can be a little diffrent then the other pokémons,but,lore friendly as well!). In exchange of the delibird candies,he gains rare candies,wich you can use to feed other pokemons!As you can see Delibird is displayed as a normal pokémon!