Howard the Duck

Howard the Duck is a humanoid talking duck that originated from Marvel Comics. He is voiced by Seth Green in Guardians of the Galaxy, and Kevin Michael Richardson in his television appearances.

Ultimate Spider-Man
In the episode "Awesome", Howard the Duck was captive in a sphere-globe in Connors' lab. He warned Spider-Man to back off and that he would use his Quack Fu, which Spidey deemed him "too weird".

When Norman Osborn is about to turn Spider-Man into Carnage, Peter imagines other possible transformations, including Howard.

Phineas and Ferb: Mission Marvel
Perry the Platypus is mistaken for Howard by Spider-Man due to Perry's possession of a duckbill.

Hulk and the Agents of S.M.A.S.H.
Howard is among the heroes captured by the Collector, who admires the "ultra rare hero", stating he's in mint condition.

Guardians of the Galaxy
In the post-credits, Howard makes a cameo in The Collector's museum remarking upon the destruction of the museum to the Collector.

Trivia

 * Howard the Duck's appearance and some of his outfit almost resembles that of Donald Duck. Because of this reason, Howard often wears pants to distinguish himself.
 * Ironically, Howard was originally a point of argument between Marvel and Disney before Disney had purchased Marvel. Due to Howard's resemblance to Donald, Disney had almost sued Marvel for copyright infringement until Howard was given a redesign to ease the dispute.