This Quilava is a fire-type Pokémon owned by Dawn. It was the Pokémon she received as egg in An Egg Scramble!.
After winning in the battle contest, Dawn received an egg as a prize. In the same episode the egg hatched, revealing a young Cyndaquil. Even though it was still young, it wielded powerful moves like Swift and Flame Wheel. Dawn chose this Pokémon to replace Ambipom (Since it is in training with the Ping-Pong Champion). Cyndaquil was pairing with Mamoswine in Dawn's latest contest where she faced Ursula and her Plusle and Minun. Mamoswine and Cyndaquil were known for their fierce-ice combo.
Prior to Dawn leaving for Hoenn, Cyndaquil and Piplup worked on a failed move. Cyndaquil wanted to come with Dawn to Hoenn and evolved into Quilava, helping her deal with a situation with some Ariados. It battled with Ash Ketchum when Dawn visited Ash in Unova.
Of all Pokémon Eggs owned by main characters, Quilava took the least amount of time to hatch, hatching in the same episode it was obtained in. The second would be Ash's Noivern.
Quilava is the eighth Pokémon to follow the pattern of premiering in a movie and then being captured by one of the main characters.
In all cases, the premiered Pokémon is not the same character as the one caught, just the same species. Dawn's Cyndaquil comes after Arceus and the Jewel of Life. This is only a technical premiere, as Cyndaquil was featured during the original Johto series as well.