Ok... no of course not
I know a penguin with a sac as its tail looks like one, but it definitely isn't one... Now I think about it, in real life Penguins live mainly on the South Pole, while Delibird is supposed to come from the North Pole (> Santa).
But no, Delebird isn't classified as a legendary, and before people are asking more of this, here follows a list with every legendary Pokemon:
- Articuno, Zapdos & Moltres
- Mew
- Mewtwo
- Raikou, Entei & Suicune
- Ho-oh & Lugia
- Celebi
- Regirock, Regice & Registeel
- Latias & Latios
- Kyogre, Groudon & Rayquaza
- Jirachi
- Deoxys
- Uxie, Azelf & Mesprit
- Dialga, Palkia & Giratina
- Cresselia
- Darkrai
- Manaphy & Phione
- Regigigas
- Heatran
- Shaymin
- and of course Arceus