Groot

"I am Groot."

- The only words of Groot's language

Groot is a character from Marvel Comics and a major character in the Marvel Cinematic Universe.

Background
Groot is a Flora colossus who at one point became a bounty hunter and partner of Rocket. He can only communicate by saying, "I am Groot," though his inflections and tone tend to convey what he means to say. Rocket often acts as Groot's translator.

How Guardians of the Galaxy Should Have Ended
Groot first appears listening in on Peter Quill's motivational speech. When Drax decides to take Quill's advice to "give a crap" literally, Groot reacts with a disgusted "I am Groot."

Groot is seen in the background in many scenes, such as the Guardians' escape from the Kyln and the Collector's deal.

During the actual ending, the original Groot has died, with a splinter from his body planted in a pot and growing into a second Groot. This Groot accompanies the Guardians at the Super Café, where he does not actually participate until Batman's conversation with Drax. Groot and Batman have a catchphrase duel, with Groot winning. Afterwards, Groot accompanies Quill as he watches several movies he missed while away from Earth, and reacts when Quill is disappointed.

On Xandar, Rhomann Dey discovers that Groot's splintered remains have resulted in multiple Groots growing on the planet's surface.

How The Amazing Spider-Man 2 Should Have Ended
Groot is seen during the credits, in which Andrew Garfield's Spider-Man joins the Marvel Cinematic Universe in time for Avengers 3.

How Guardians of the Galaxy Vol. 2 Should Have Ended
Baby Groot is first seen in Ego's brain as Rocket instructs him to handle a bomb. Groot presses the button that activates the bomb and accidentally kills Rocket.

Groot is then seen agreeing with the Guardians on how Rocket got himself killed by the Sovereigns, and accompanies Rocket during his escape from the Ravagers.

During the final battle, Ego leaves Quill to deal with Groot and the bomb and easily throws them both out of his brain.

Groot accompanies the Guardians at the Super Café, once again having a catchphrase battle with Batman and Yondu.

How Avengers: Infinity War Should Have Ended
A teenage Groot joins the Avengers and Guardians at the Super Café, but is engrossed in his video game and does not care about anything anymore. His nonchalant "I am Groot" provokes Batman to attempt to start another catchphrase duel, only to come up blank.

Trivia

 * As a running gag, Groot and Batman tend to have a catchphrase duel between Groot's "I am Groot" and Batman's "I'm Batman."
 * Groot's death in Infinity War is homaged in its HISHE, with Bowser dying in a similar manner to Groot.
 * In How Teenage Mutant Ninja Turtles: Out of the Shadows Should Have Ended, Vin Diesel makes a cameo and shouts Groot's catchphrase, a nod to himself playing Groot in the Marvel Cinematic Universe.