Not much is currently known about Y'Gythgba's history prior to meeting the turtles aside from the fact that she is a highly trained lieutenant of the Salamandrian air fleet. She travels with her mentor and partner, Commander G'Throkka, who assists her in their many conflicts against their race's arch-enemies, the Triceratons.
The Moons of Thalos 3
Y'Gythgba and G'Throkka lead an attack on the Triceraton Mother Ship after they manage to sneak by the Triceratons security measures. Around the same time, Fugitoid's ship, which was carrying the turtles, April, and Casey at the time, accidentally lands in the Triceratons' territory after a tachyonic warp Fugitoid used to get away from Lord Vringath Dregg. Captain Mozar is soon aware of both enemies' presence and deploys forces to destroy them.
The Triceratons manage to badly damage the Fugitoid's ship, sending it spiraling out of control. This caused the Ulixes to crash into Y'Gythgba and G'Throkka's ship, subsequently damaging it as well and causing both ships to crash land on an ice planet. Both groups simultaneously learn that irrilium, a metal that can be used to repair their ships, is nearby and realize that they must go after it before their astro suits run out of heat and oxygen. G'Throkka and Y'Gythgba soon learn that the ones who caused their ship to crash are also heading for the irrilium. Despite G'Throkka's instant respect towards them, Y'Gythgba suggested that they must destroy them and take the irrilium for themselves, as their punishment for costing them a possible victory against the Triceratons. Y'Gythgba decides to act on that motive and confronts the heroes, believing them to have purposely rammed their ship. Fugitoid assures her that is was not their intention to damage their ship and tries to cooperate with her. It seems to be working until Leonardo extends his hand for a handshake, which is the Salamandrian symbol for combat and it prompts her and G'Throkka to start attacking. After she knocks Donatello and April down, Raphael tries his hand against her. He is quite easily outmaneuvered by her and is hit very hard in the process, which resulted in Raphael developing a crush on Y'Gythgba. Y'Gythgba took advantage of his dazed state to knock him and Donatello out. After Y'Gythgba and G'Throkka defeat the teens, Fugitoid attempted to ward them off with his blasters.
But Y'Gythgba throws an explosive disc at a glacier behind him, causing an avalanche to fall over the heroes. G'Throkka insisted they dig them back out so the don't die with such dishonor, but Y'Gythgba reminded him that they are running out of time and must hurry to the irrilium. Sometime after they are dug out of the ice, Raphael still has Y'Gythgba on his mind and even asks Casey if he thinks a turtle could date a newt, to which Casey laughs hysterically. Raph tries to convince everyone that the Salamandrians may not be as bad as they seem and "the lizard girl is cool." Leonardo denounces that idea and Mikey is surprised to hear this as he asserts that she bigger, stronger, and probably a better fighter than him. Raphael points out that it is precisely the reason he likes her. Meanwhile, G'Throkka learns that they have survived the avalanche and asserts that they should not to be enemies. But Y'Gythgba tells him that they fight dishonorably and are "clearly" working with the Triceratons. However, G'Throkka tries to avoid any more confrontation and tells Y'Gythgba to follow him toward the irrilium. Raphael catches up with them to try cooperating with them despite Leonardo discouraging him. Y'Gythgba rejects his offer of working as a team, but blasts the ice at his feet, causing him to fall rather that simply shooting Raphael, which G'Throkka finds interesting. Right as Y'Gythgba tries to deny that it meant anything, they are ambushed by a horde of ice dragons. The two Salamandrians valiantly fought the creatures, but to Y'Gythgba's horror, G'Throkka was frozen. As Y'Gythgba was knocked down by the creatures, Raphael came back and slayed the dragon dragons, saving her life. Y'Gythgba quickly returns the favor by shooting an ice dragon behind Raphael and then tells Raphael that he truly is a noble creature. They both introduce themselves, and Raphael has trouble pronouncing her name.
He then asks if he can call her Mona Lisa in admiration for the picture of the most beautiful woman in art. Y'Gythgba agrees, and she comes close to Raphael and asserts that one day their noses will meet in the flesh, which causes a lovingly dazed reaction from Raph. They then turn to the frozen G'Throkka to which Mona Lisa decides use a low energy output to thaw him out rather quickly. After G'Throkka is successfully thawed out, he, Mona Lisa, and Raphael save the turtles, Casey, and April from a horde of ice dragons and assist them in fighting the creatures. With a team effort, they all manage to destroy the dragons. Afterwards, the two teams merge as one, becoming friends, and decided to search for the irrilium together. After Donatello finds a Triceraton space mine containing the irrilium, they are ambushed by yet another horde of ice dragons. Mona prepares to fight them again, but she and the others follow Raphael's idea to run straight for the Ulixes with the mine. Raphael, Mona Lisa, Fugitoid and G'Throkka lift the mine as they are running away from ice dragons. After Donatello and Casey mange to lose the creatures in an avalanche, they make it to the Ulixes, but their heat and oxygen finally begins to run out. As Fugitoid tries to quickly repair the ship, the turtles, humans, and Salamandrians begin to faint one by one due to lack of oxygen. Mona Lisa and Raphael are the last ones conscious but are dying from lack of heat and oxygen.
Raphael tells Mona that he wishes he could tell her how he feels. Mona hugs her tail over his shoulder and tells him she already knows, and they both finally faint as well. Raphael wakes up in the repaired Ulixes to sees Mona Lisa standing over him and calling his name. She helps him up and they exchange loving expressions as G'Throkka thanks all of the heroes and hopes to one day return their kindness. Mona agrees and holds Raphael's hand, and both start to lean in for a kiss, but they are interrupted by Professor Honeycutt, who tells them that he has repaired the Salamandrian's spacecraft and they must leave quickly in order to catch up with the Triceratons. Despite this, Raphael still tries to tell Mona Lisa his feelings for her, but stumbles over his words trying to do so. Mona lovingly shushes him with her finger and tells him to let her say it for him in her own language. After she does so, she grabs Raphael and kisses him on the lips, causing a mixed (but mostly positive) reaction from the other heroes. As the Salamandrians are about to leave, Y'Gythgba waves him goodbye, and Raphael is left in a saddened state, hoping to one day see her again.
The War for Dimension X
Mona Lisa and Sal Commander next appear in Dimension X, trying to strike a truce with the Kraang to have a formidable ally in their war against the Triceratons. As their representative, Kraang Subprime passionately refuses, telling them that the Kraang invade other planets to avoid the Triceratons. Despite Mona telling him that avoiding the fight will bring dishonor to his species, Subprime begins to leave saying that honor does not concern him and that it is best for them to look for the next planet to mutate. Mona is disgusted by such remarks, but G'throkka reassures her that they will find other allies. When Mona suggests allying with the Turtles again, Kraang Subprime overhears this and orders his forces to subdue the Salamandrians, as he says any ally of the turtles is an enemy of Kraang Subprime. They succeed and threw them in their dungeon, creating bad blood between them and the Kraang. After Raphael and "Savage" Michelangelo sneak through one of Kraang Subprime's portals, they pass by the Salamandrian's cell. When Raphael became angry that he lost Queen so quickly, Mona overheard him and called out to him. Raphael immediately rushed to her cell to break her out and gets the door open. He then asks what she was doing there and that he thought he would never see her again, but Mona simply replied by lifting him to her face and kissing him. When Mikey interrupted their "kissy nosing" saying that they must rescue the Utrom Queen, Y'Gythgba and G'Throkka tells him that the Utrom and the Kraang are one and the same cannot be trusted. Raphael tells Mona that he was skeptical at first as well, but the Utroms helped him. As Mikey was failing to convince G'Throkka that the Utroms were good Kraang, Raphael tells Mona that he would never do anything to hurt her. Mona then tells Sal Commander that she once doubted the Turtles even though he insisted otherwise, but she now trusted Raphael with her life, and completely believes him. Sal Commander submits to this, and reluctantly agrees to help the save the Utrom Queen. Raph and Mona then kiss again, causing Mikey and Sal Commander to facepalm. The four of them proceed the break into the top floor of Subprime's lair and recover the Utrom Queen. They apparently have Subprime surrounded, but he releases a large Draco droid to attack them.
However, the Utroms find them and blast a hole in the wall that hits both Subprime and the Dracotroid. Mona, Sal, Raph, and Mikey look down from the hole to see that the Utroms, Leonardo, Donatello and The Fugitoid have come to rescue them all. The Dracotroid then got back up and blasted the four off the building. Mona was caught by Raphael as Sal and Queen were saved by Mikey. Mona then proceeds in aiding the Turtles, Utroms, and Fugitoid in the fight against the Kraang. When Raphael gets grabbed by the Dracotroid, Mona saved him. Raphael told her that she learned some new moves since he last saw her, to which Mona says that she could teach them to him one-on-one, which excites Raphael. He soon fell off the Dractroid and it crashed, sending Mona into freefall from extreme height. Raphael misses catching her but quickly used a Long-Tongue Worms to save her, which quickly made him change his negative opinion about Dimension X. After the Kraang are defeated, Mona starts to perform operations on her ship and is approached by Raphael, who asks her that if they are on the same planet again, if she would like to go out sometime. Mona was confused by this question and asked if he meant go out to space, but she retorts and says that she will go with him anywhere. Their affection confused Leo, but Mikey said that now was the perfect time to "kissy nose." This angers Raphael and he starts walking towards Mikey to hit him, but Mona pulls him back and passionately kisses him.
The Evil of Dregg
Mona Lisa sends a distress signal to the Ulixes, informing Raphael that Sal Commander has been captured by Armaggon. Shortly afterwards, she catches up to the Ulixes and boards the ship, with her and Raphael ecstatic about seeing each other again. Mona tells Leonardo the Sal has been sent to Sectoid 1, prompting Fugitoid to believe that Lord Dregg is holding him captive. Both Leo and Raph assure her that they will find Sal Commander, as he is one of them, and Mona thanks them all. After locating Dregg's headquarters, Fugitoid navigates the ship to the Sectoid system, landing on Secoid 1. Everyone exits the ship and Mona begins to lead them to the Dregg's lair. After fending off an attack by a swarm of alien wasps, Donatello is badly stung, so Fugitoid and April take him back to the Ulixes while the rest of the team kept going. They finally make it to Dregg's lair and stealthily moved through it, searching for Sal Commander. Michelangelo spots him lying on the ground and attempts to get his attention, but it turned out to a bubble trap triggered by his hologram and captures Mikey and Casey. Lord Dregg and Armaggon then reveal themselves, and in saying "You've done well, Y'Gythgba", Dregg reveals that Mona Lisa purposely led them to the trap for Dregg, causing confusion and heartbreak to Raphael. Mona was unresponsive to Raphael's plea for an explanation. Leo orders Raph to free the others while he fights the Vreen, but Raphael was in too shocked of a state to even move. Leo manages to take out a few Vreen before being shot down by one, and Armaggon takes advantage of Raph's emotionally weak state and beats him up, with both turtles being captured as well. She and G’Throkka then tell Dregg that it is now time for him to hold up his end of the bargain and discuss the terms of their home world.
Dregg accepts and call them to talk in private. Before Mona leaves, she looks back at Raphael, who gives her a distant glace in return. Sal Commander tells Dregg to call of his attack fleet on their home world of Salamandria, and Mona says that he promised he would not do so if they brought him the turtles. Dregg tells her that he already released her commander and will still attack the planet. Mona then realized that her sacrifice was in vain and painful regret of her actions. Meanwhile, Leo, Mikey, and Casey manage to destroy the bubble encasing them and begin fighting Armaggon and the Vreen, while Raphael still cannot focus. Dregg quickly shows up and beats the heroes, throwing them down a pit, to the horror of Mona Lisa and Sal Commander. Mona then decides to try to sneak an attack on Armagaan, but he blocks it and the Vreen restrain the Salamandrians. Dregg states they he will feed on them and their planet will be a smorgasbord for his species. Luckily, April Donatello, and Fugitoid come to her aid, unaware of what they did. Donatello kills the Vreen guarding them and comes to Mona's aid, asking if she is okay, to which Mona states that she has failed him. When Donatello fends off more Vreen, Dregg shows up and tries to eat him, but Mona strikes Dregg in the back to stop him, declaring that she intends to rectify her terrible mistake. After temporarily neutralizing the threats, Leo orders everyone to get back to the Ulixes. Raphael struggled to climb his way out so Mona lifts him out of it, only to get her hand slapped away by an angered Raphael. Mona then apologizes for not telling him he truth, but Raphael expressed that she betrayed them when he trusted her the most. The team heads back to the Ulixes and are being followed be Dregg and his army, including the gigantic Scorpinoid. Mona Lisa and Sal Commander ready to battle them and tell the turtles to leave the planet, as they will hold of Dregg's alien armada.
Donatello asked what would become of Salamandria without them. Mona Lisa simply told him to go and save his own world, and then told Raphael that she will always love him, before charging in to battle Dregg's army. Hearing Mona say that she loves him reignited Raphael's fighting spirit, causing him to charge in with them, beating a majority of the Vreen. Shortly after, Mona gets stabbed in the back by the Scorpinoid causing her to fall unconscious. Raphael manages to reach Dregg using it's stinger and singlehandedly took him out. Afterward, he frantically rushed to Mona's aid, promising her that she will make it. She later wakes up in the Ulixes, being treated by Fugitoid and surrounded by her allies. Sal Commander states that though it is impossible, he asks the turtles for forgiveness. Mona reiterates this to Raphael asking if would ever find it in his heart to forgive her. After a short pause, Raphael touches her hand and lightly smiles, prompting Mona to do the same, and they both lean in for a kiss.
As a Salamandrian space fleet lieutenant, Mona Lisa is no stranger to weapons and is heavily armed at all times. Her known weapons are:
Laser Sword - Mona's signature weapon. It is one of her main tools in close combat and appears to be able to cut through anything.
Explosive Discs - Flat, moderate level explosive discs with sharp edges that can be thrown and timed to detonate.
Astro-suit - Mona Lisa's astro suit is a hard exoskeleton built to help her survive and fight in off-world locations. The suit is also equipped with several weaponry functions. Among them are:
- Morphing Pads - The pads on the back of Mona's forearms can change form to become weapons, such as plasma blasters, axes, etc.
- Tail Spikes - The suit also has spiked extensions to fit for Mona's tail to make her tail attacks even more deadly.