What will the plot be for the 3rd film?

I picture a martial arts tournament.

Po and the Furious Five enter to represent their dojo with Shifu watching from the royal box alongside the other Masters, including the host; An elderly Lion whose apprentice's are also his Lioness pride.

One of the opposing dojo's is almost reptile-exclusive, and is composed of a Chameleon, a Frilled Lizard, and a terrifying Komodo Dragon, their master is a bullfrog who sits silent and impassive beside Shifu. Also of importance are a Sumo Wrestler Elephant and a master swordsman, media hound, and self-proclaimed ladies man Fox.

Po, Tigress, Monkey and Viper make it through the second round against unimportant opponents. Mantis quits because he thinks his opponent, a female Mantis, wants to eat his head, and Crane engages in a waiting game against a camoflaged Chameleon, flying overhead for so long that night falls and he eventually falls from the sky snoring to be gently pushed out of the square by Chameleon to a very small, tired crowd. Monkey defeats Frilled Lizard when Lizard uses her frill in a cloak and dagger way to thrust knives at Monkey, only for them to be snatched away, when Monkey is left holding a knife everywhere but his right foot, which he's standing on, Lizard admits she only knows weapons techniques and is declared the loser.

In the second round Po manages to beat Elephant despite him being beaten at his own game (namely bouncing people) by stowing a dumpling disguised as a mouse in his mouth that he scares Elephant away with. Fox and Viper engage in a sword/tail fight with Fox flirting the whole time and Viper slowly being charmed by him, resulting in her wrapping round his neck, kissing him full on the lips, and then spinning him out of the square like a top off the square as he clutches his heart with love.

Tigress vs Komodo is declared, and it is the fight everyone has been waiting for. It is INTENSE as the two claw, kick and bust out amazing Kung Fu, made more difficult when they discover that Komodo's drool is highly acidic, making her have to dodge flying trails of the stuff. At then end Komodo has her in a painful submission, when he asks Tigress if she yields and she replies 'Never!' he says 'Good.' and we watch the horrified reactions of Po, Shifu and the rest as a crack and Tigress' scream of pain echo through the dojo. Komodo walks away chuckling cruelly to himself as bells ring for the medics and the tournament is finished for the day, meaning Monkey advances by default.

We find out in the hospital that Komodo broke Tigress' leg, and Po admits how scared he was for her, and Tigress asks him to stay as the Nurse goat starts butting them out for overstaying visiting hours. Viper heads to Fox's room to ask him out but insteads finds him, Komodo and Lizard in fierce debate about their plan: The Dojo and the Lions who guard it were built upon the sealed lair of a Dragon who led a cold-blooded army in a genocidal campaign against birds and mammals, before being defeated by the original Dragon Warrior. Using the tournament as a front, they have uncovered the hidden entrance and have gotten all their strongest rival in one place, using the blood of the Dragon Warrior (Po!) they will unleash the Dragon and create a cold-blooded utopia devoid of warmbloods. Viper stealthily hears all this and is about to make her escape when Chameleon reveals himself behind her and slips a sock over her head, catching her.

Tomorrow the last match of yesterday plays out with Monkey losing to a Serval. Po is pitted against Komodo, Po talks big about making Komodo pay for what he did to Tigress, but instead of replying Komodo picks his ear and bows to show the Bullfrog master rising to his feet and making a croak so loud and prolonged that it knocks Po and the entire audience unconscious, with Po seeing Komodo walking toward him as he faints. All the way over in the hospital Tigress wakes in pain but not overwhelmed by the noise, and looks with concern out the window.

Po wakes up bound in a dank tunnel with Monkey and Viper beside him, who he nudges awake, the cold-blood dojo and Fox are already there looking for the panel that needs Po's blood. As he has no idea what's happening he openly asks and Viper summarises their insane plan, then asks Fox why he's going along with it, to which he replies that being the last living Mammal would be a crowning achivement for him, he goes to kiss Viper but she bares her fangs at him.

After this Po turns to Monkey and asks if he's heard all he needs to, Monkey replies yeah and the three of them spring up with their bounds untied "Seriously, ropes?" the two sides rush at each other in a big fight scene in the tight space with Viper sticking the sock she was caught with into Bullfrog's mouth sop he can't perform the same trick again. Though it looks like its winning when Po catches one of Komodo's punches the claw of him thumb pricks his palm and a single bead of blood runs down his claw and drips dramatically to the floor as everyone stares at it. With a splash the entire room begins to shake and the wall collapses with a rush of air. The two sides look into the pitch black, one eagerly the other apprehensively, when an almighty roars comes from within coupled with two huge deep red glowing eyes, another rush of air accompanies the roar but this time vines and tropical trees start growing out of the floor and walls. Suddenly a tide of snakes of all types rush forth and carry everone but Po out of the tunnel and out into the open. As the Dragons huge footsteps start getting closer Po dusts himself off and gets into his best fighting pose.

The whole thing devolves into a massive melee outside as the waking contestants and hosts realise the invasion is happening, so its an assortment of creatures vs the Snake army. Tigress appears on a crutch with her leg in a cast delivering swipes with one and stiff kicks with the other with a cry of "Ow!" every time. Mantis and not-Mantis find themselves fighting back to back very effectively with them sharing a smile amongst it all. Shifu and the Lion prepare to face off with Master Bullfrog only for him to throw his hands up and admit he doesn't know Kung Fu, he's just a member of a chorus! Viper is holding her own when Komodo swipes the snakes away and stands on her, her fangs scraping harmlessly off his scales. With a 'if you're not with us, you're against us' line he goes to slash her in two only to have his axe parried by Fox, who shows his worth forcing Komodo onto the backfoot with slices and jabs, a blow of his tail sends the sword clattering, only for Elephant to barrel through to send him flying sideways, as he lands on his feet he flicks streams of acid drool at them only for Crane to swoop in and drive them backward with a flap, scorching Komodo's skin. Mantis and monkey double team him, sending him into a flying spin that lands him on his back, where he looks up to see Tigress standing over him, before she brings her leg cast crashing down on his head knocking him out. Of course that hurts her so much that she goes stiff as a board and Crane and Monkey have to carry her out after they all rush to congratulate her. Viper turns looking for Fox but he and his sword are both gone.

With most of the snakes defeated and the crowd cheering, Monkey suddenly realises "Oh no, we have to help Po!" Crane asks what Po could possibly be dealing with that is worse that what they just went through when Po smashes through the floor of the square riding thr snout of the Dragon, which is so large that it could swallow him whole. It's a typical Chinese Dragon, multi-coloured, snake-liked with whiskers and no wings. As it rises from the ground Po does a jumping hand stand and gives it a left hook that snaps its head round and sends him cartwheeling toward the ground. The protagonists rush to help him but are halted by Shifu who says that he must defeat the Dragon alone, it's his destiny as the Dragon Warrior. Its a helluva fight with Po ducking and rolling to avoid being eaten, holding the Dragon's jaws apart, and holding the whiskers like reins as he rides it up into the sky, where grabbing the ends of iits whiskers he spins it around, with the serpentine body making a loop round the sun before hurling it back to the ground like a snaky missile. po falls back to earth riding the knocked-out Dragons coils like a slide and flying off its head to land butt first infront of the agape crowd
"I am NOT dragging that thing into that cave alone!"
and he collapses onto his back with a phew.

As the only only challenger to win a fight during the tournament final, the Serval that beat Monkey is declared the winner with wild celebrations, the Lionesses are shown rebuilding the wall of the cave while one hangs a 'Dragon Warriors Keep Out' sign at the entrance to the tunnel, and the protagonists, plus Mantis' new girlfriend, set sail home on a river barge, with Po and Tigress lying side by side on the deck, her in her leg cast and neck collar, him wrapped nearly head to toe in bandages, they look at each other and slowly with a lot of eeing and ouching, manage to hold hands. They Smile at eachother and gaze out over the famous Li River view as the sun sets.

The End