This special debuted shortly after the debut of the feature film Les Gardiens de la Galaxie (2014) which features Groot and Rocket Raccoon. They are depicted here as a team of bounty hunters and have not yet joined up with the other Guardians.
Reptil appears in this special as a "Junior Avenger" being trained by the veteran heroes. Not to be confused with Reptyl, a long time enemy of both the Avengers and Silver Surfer.
The green woman to whom Tony gives a small box is She-Hulk, Hulk's cousin. In the comics, she and Tony have a romantic relationship.
Believe it or not, Santa appearing in this special is actually supported by the comics, as he has been established as real in the Marvel Universe.
The characters, along with Avengers Tower, are modeled based on how they appear in the movies. As of yet, Reptil has not appeared in a movie.