Altaria is a blue, avian Pokémon. Its body and cloud-like wings are covered in fluffy, white feathers. It often folds its wings behind it, obscuring its back. Two long, blue plumes extend like streamers from the back of its head. It has a short, hooked beak and prominent cheek patches, both of which are white. Additionally, it has beady, black eyes. It has a long neck and short legs protruding from its fluffy body. The feet are blue with four toes, three claws forward, and one backward. The tail is made up of five feathers, the outer two being longer than the inner ones.
Mega Altaria has more extensive cloud-like plumage, with a large, fluffy mass extending from its back. The feathers have grown as a self-protective measure, and they glimmer with an iridescent sheen. Its cottony wings are more distinct than in its base form, and its blue belly is now exposed. Additional fluff surrounds its neck like a collar, and its head is adorned with a hat-like crest. A single, small feather curls out from its forehead, though its facial features are unchanged. Its tail feathers have grown into a long, wavy streamer, with three longer central plumes. Mega Altaria's singing voice is even more beautiful than that of its regular form. It is known for its sociable personality and is not timid.
This Pokémon uses its wings to catch updrafts and soar across the sky in a calm and graceful manner. It gracefully glides through the clouds, often while singing or humming in a soprano voice. Its voice seems to have special properties that induce a dreamy state for listeners. Altaria can be very affectionate, enveloping people it has bonded with in its cotton-like wings. While normally kind, Altaria can attack foes with shrill cries without mercy if provoked. Altaria is often found living in forests, though it also inhabits mountain ranges.
Altaria is likely based on a Peng, a Chinese legendary bird of enormous size, said to travel 3000 li in one flap of its mighty, cloud-like wings. It is often portrayed as having a fish's head and whiskers. Altaria also resembles a cockatiel, albeit with clouds as wings. Similar characteristics shared with cockatiels include its crest and "cheeks". The resemblance is further expanded upon by Altaria's Shiny form resembling a lutino cockatiel, which is famous for its mostly white and yellow coloration.
The shape of the fluff on Mega Altaria's head may draw inspiration from dutch caps or ushankas.
Altaria may be a combination of alto (Spanish, Portuguese, and Italian for high; musical part between tenor and soprano) and aria (Italian for air; musical piece for a single voice). Both words being terminologies used in music relate to Altaria's singing abilities. The name may also refer to the star Altair, the brightest star in the constellation Aquila with the latter's name being the Latin word for eagle.
Tyltalis may be derived from チルット Tyltto (Swablu). It may also be a reference to the play The Blue Bird (L'Oiseau bleu) by Belgian playwright Maurice Maeterlinck, featuring two siblings named Mytyl and Tyltyl tasked in finding the bluebird of happiness. The latter half of the name may be derived from cockatrice, a mythical creature with a draconic or serpentine body and a rooster's head. It may also involve チル chiru (Ryukyuan for crane) or Tyl (alternate name of the star Epsilon Draconis, located in the constellation Draco).