Gon Gon was the principle Monster of the Week on Ep.34 of UFO Robot Grendizer. Piloted by Commander Goss, an Elite from Planet Wolf sent by King Vega to kill Duke in exchange for the Freedom of his home world. It had a humanoid appearance, with a normal left arm with hand, while the black right arm ended on a Crescent Blade attached to it. It's head was adorn with four curve horns and its face was black with a orange shield for the cockpit, with light yellow eyes. Beside the blade, it could fire a pink laser beam from the yellow plate on the chest (like the Mazingers with the Breast of Fire) and optic Beams. The Body scheme was Purple, Dark Purple, Purple Red, Orange, Yellow and Black in color. The Vehicle form was a basic Orange color Saucer Disk, the shells of it will be hanging on the sides of the Monster's waist.

A new Ship arrives to the Skull Moon Base, piloted by Commander Goss from Planet Wolf, Zurin and Gandal head to recieve him when they learn he had gone to the Computer Room, where they find him looking at a picture of Duke Fleed: Protesting the insolence, The Commander (young and arrogant) finds no time for petty formalities, taking only focus on his mission and leaves, Gandal wants to teach him a lesson sents out the Saucer Beast Gome Gome, who surprises him and open fire: the Beasts transform, but Goss ends Gome fast by slicing it in half and continues his way to Earth. King Vega drops in and informs them he took the mission for the freedom of Planet Wolf if he is able to kill Duke in 3 Days time. Zurin's brief on the Planet shows it to be a barren world of rocks and desert, with no plant life growing on it, as he strength gets greater under a full moon.

Goss makes it to Japan and attacks a Dock refinery: Gon transforms to ravage the area, the event been watch in the lab By Umon, Daisuke and Koji: Daisuke departs on the Grendizer to confront the invader. Once as he arrives, Goss identify himself and challenges Grendizer and rapidly attacks, Grendizer barely avoiding it, but Gon maintained the pressure on his enemy thanks by the pilots skills, avoiding all attacks, firing at him hitting and kicking him, not allowing Duke to react, having the advantage, and when is about to strike the death blow, Goss stop. In a shock to Duke, Goss tell him he would defeat him when under the Full Moon, explaining his people were conquer under the Full Moon, hoping to turn the moment of their greatest defeat into a victory for them. Duke leaves and returns back to Base: the first time he was defeated under the terms of another Warrior. He later explains to Umon the situation and proceeds to think of a plan, though recognizes Goss as a true Opponent.

Later, a new cowboy shows up ridding into the Makiba Farm, Goss in human disguise, and while playing a harmonica, explains (quite brazenly, I might add) he is after his enemy: Duke Fleed. Goss takes notice of Hikaru's reaction (of course she knowing of his true identity). Hikaru then heads to the Observatory and informs Daisuke, he concluding he is to observe him until the Full Moon. Koji takes off to challenge Goss, only to be beaten by him fast, Daisuke arrives and tells Dambei to take him to the Observatory, he then asks for a private conversation with Goss.

In the woods, Daisuke tells Goss to not hurt anyone else, the latter recognizing on Equal Terms, then throws a knife at Daisuke which he avoids only hitting a petal. Duke asks Goss if he does believes King Vega would "uphold his promise?", Goss answered he lived with Wolves on the Rocky Mountains and learned their Moves for the sole purpose to defeat him for the freedom of the Wolf Planet. He then challenges Daisuke to a knives fight though Goss again demonstrates he is a more adapt fighter; the fight is however halted by Hikaru who intervenes, and despite he pointing the knife at her, Goss calls out the match, still the final battle is still on tomorrow. This leaves Daisuke with doubt in his thoughts.

The next day, Hikaru asks for Goss help to search for a strayed Horse, during search, she tries to convince him that if he kills Duke, Earth falls on the hands of Vega, however this is not of his concern. At a water fall, Hikaru makes her move and points her hunting riffle at Goss, though he wounds her with a dart been spring from his harmonica falling from her horse; Goss then slaps her for her lying. Daisuke arrives later to see Hikaru tied to a branch on the Waterfall. He and Goss fight close to the cliff and the later falls into the Rapids below.

Yet, surpringly, Daisuke jumps to save him from drowning and takes him to the farm. Wondering "why he saved him?", Hikaru replies "He behave with the inspiration of his manners". She leaves and Goss sees the flowers and he is reminded in a flashback, when Planet Wolf was blush place, and as well on his young sister Ronan, just before the invasion, blaming King Vega for the dead state of his world and the death of his Sister. Goss then escapes with all of these thoughts on him mind, knowing the fate that would await Earth, when Gandal signals him a squad of Minifos are on their way to back him up. Duke flies to receive them and dispatched the number, but is outmaneuver by them when Goss on Gon Gon arrive to destroy them, wanting to kill Duke himself.

The two transform for their final battle: but fighting under the light the Full Moon, Goss and his Mecha are far more stronger and agile than in their first encounter, able to deflect all of Grendizer's attacks. Duke continues firing at Gon and noticed something: he uses the shoulder blades, and runs towards Gon Gon, these hit it, bounce back, Duke creates the Double Harken and impales the Beast in the mouth plate, hitting Goss in the chest with the very tip of the blade. The Beast falls and Goss comes out, he walks towards Grendizer and flower patch.

Duke realizes he gave up on purpose despite his eagerness for killing him. Goss kneels and holds on to the flowers, and in the final moments of his dying delerium, sees (confusing Hikaru with) his sister, Ronan, calling out to him. Goss extends his arm to her, sucumbs to his wound and finally dies, everything ending in the best condition. Duke realized Goss' love for Flowers and promises him to continue on fighting so life remains on Earth as a shooting star blazing the night sky. Perhaps a metaphoric way to say Goss' spirit has heard Duke's words.

Side Note: Hands down, I would say Goss was by far the best written character the pilots Vega has sent, his motives are the quite frankly the most pure and noble, even though is obvious Vega is just using him, and chooses to die so Earth doesn't fall to the same fate of a barren wasteland as Wolf did, even though this maintain his planet under the enslavement of Vega. He is right there with Dinobot from Beast Wars and urVa the Archer from the Dark Crystal Age of Resistance, and it is quite unfortunate he gets only one Episode. If Grendizer is ever rebooted, considering we get a rehash of the Mazinger Z show every decade, I do hope for him, as well Capt. Gorman and Commander Minao, getting extra episodes before they are bumped off, cause they had been by far my favorite pilots and I know they are still more to come. Also, watching the episode the 2nd time, it hit me they (the producers) were doing a Clint Eastwood/John Wayne nod in his cowboy disguise. I dunno, I guess is just me, but that was the thing it was getting to me.