Warning: SPOILERS for Mech Strike: Monster Hunters #5Marvel's his fellow Guardian Rocket Raccoon, and his extremely limited vocabularly: he can only say "I am Goot" (and only those words in that exact order). But Mech Strike: Monster Hunters #5 depicts Groot in a form unlike any other - save for his very first appearance, long before he became a Guardian of the Galaxy.
While Groot did not officially the Guardians of the Galaxy team until 2008, his mere existence predates the entire team (both the original and modern incarnations). First appearing in Tales to Astonish #13 written by Stan Lee, Jack Kirby and Larry Lieber, Groot appeared as a massive tree-monster from another world who terrorized a small town - and he could speak in full sentences as well. Hailing from the mysterious Planet X, Groot controlled the trees around him in an attempt to capture humans for study, but he was defeated by termites harnessed by a human scientists, and Groot was dead - at least for a while.
In Mech Strike: Monster Hunters #5, written by Christos Gage with art by Paco Diaz, the evil Doctor Doom has harnessed the power of the Eye of the Kraken to transform into a massive monster. While the other Avengers have transformed into similar monsters, none of them can defeat Doom on their own. With a suggestion from Groot ("We are Groot", echoing the line in 2014's Guardians of the Galaxy MCU film), the Avengers all combine their mech forms into Groot and control him as one controls a Power Rangers-esque Megazord.
Groot Has A History Of Being A Giant Monster
Unfortunately, Doctor Doom exploits Groot's many pilots to defeat him rather easily. "Too many hands attempt to guide your wooden puppet!" he says as he easily dismantles the Avengers' defense. Thankfully, the Wasp shrinks to remove the Eye of the Kraken from Doom's monstrous body and the Latverian dictator is defeated. While Groot rarely grows his entire body, he does have the ability to lengthen his limbs to appear taller than he actually is (though this power isn't quite the elastic ability of the Fantastic Four's Reed Richards, it is similar in functionality enough).
It must be noted that Groot's power in this issue came directly from the Eye of the Kraken working in conjunction with the other powers of the mechanical, monstrous Avengers. Unfortunately, he may never grow to be this giant again. This sits fine with the usual peaceful Groot, who is content to protect his friends rather than exchange punches with Doctor Doom - but he will gladly step up to fight if necessary.
