You Ain't Got No Legs, Leutinet Dan
Once upon a time, Princess Luna was sitting in her royal bedchambers drinking tea when all of a sudden, Princess Celestia burst in through the window and was all like, "Hey, Luna, remember that movie, Predator?"
So Luna said, "For the last time, I was banished on the moon during the 80s, of course I don't remember Predator"
Then Celestia replied, "Well too bad, 'cause I found him and now he wants to fight"
At that exact moment Predator kicked down the door and did that roar that Predator does where his mouth opens up in four pieces and he was all 'AAAHHHHHH!!!' and Luna freaked the hell out 'cause she never saw the movie Predator and that thing was freaky as heck.
She jumped in the air and screamed and starting throwing all her teacups at the freaky alien dude, which you should never do because Predator takes that as a sign of aggression. So now Luna's yelling and Predator's yelling and also swinging his arm claws around trying to slice Luna, and Princess Celestia is on the ground laughing and she laughs so hard that she accidentally summons the Element of Laughter, so now Pinkie Pie is there and she brought a pair of socks just so she can laugh her socks off which is exactly what she does.
Meanwhile, Predator gets the bright idea to use his grapple hook which I'm not even sure he has and I might be confusing with Schwarzenegger's trip wire but I haven't seen that movie in like three years, and anyways, he grapples Luna down to the ground and now he's charging up his shoulder cannon, but lasers always take forever to charge when they're pointed at the main character, so Luna uses the opportunity to drag Predator and herself to the balcony where she throws herself off since she has wings and all that junk.
But Predator is still grappled onto Luna so no flying today, and now they're fighting in midair like a couple of ninjas, and the wind is going past all 'whoosh' 'cause they're falling really fast, and the clouds are flying by and pegasuses are flying by like, What the heck is the princess doing now?, and to answer their question, the princess is busy karate-chopping Predator in the neck, but the Predator is actually the alien-predator from Alien vs. Predator 2, so he's got one of those mouth-inside-a-mouth things and he's trying to bite Luna in the face like chomp! chomp! chomp! so she's just having a really bad day.
By now they've fallen so far that they are actually outside of Canterlot since you know Canterlot is this big city hanging off the side of a mountain, and they've actually left the city and are just falling down the mountain at this point.
So now they're pretty much at the bottom of the mountain and they hit a cloud, and Luna has wings and pegasus powers so she actually is stopped by the cloud but Predator falls right through and lands on this ginormous palm tree that breaks his fall somehow, and then he bounces off the tree like it was a catapult and does this double frontflip in the air before landing on the ground and escaping into the jungles of Vietnam, because Vietnam is actually in Equestria and it's a jungle at the base of Canterlot.
So Luna's on that cloud and she's got a headache like nobody's business, and Celestia flies down and is all, "You know, he's probably gonna go to Ponyville and do evil Predator things unless you stop him"
So Luna is like, "Ugh, I guess I'll go vanquish Predator if I have to", and then she flies down and now she's in the middle of Vietnam and all the Vietnamese people are there eating noodles with Sriracha sauce, but Luna doesn't like spicy food so she can't eat any of it which sucks 'cause she missed breakfast.
So while she's down in Vietnam haggling over the price of a roast duck that she doesn't even want, she's see's like these three laser dots scan around and stop on the face of the old dude she's arguing with and she's like, Oh no, I've never seen the movie Predator but am 100% certain that that's the targeting sight for his laser cannon.
So she tackles the old guy at the last second before this big energy ball flies over their heads and explodes a POW camp since Vietnam is full of those, and now all the Vietnamese people are running around screaming and Predator is just firing off laser balls left and right, so now Luna is flying around trying to protect all the civilians with her magic shield and in the midst of all the chaos and confusion she feels a hand grab her shoulder from behind and it's Arnold Schwarzenegger and he's like, "Come with me if you want to live", which is the wrong movie but Luna never saw Terminator either so she runs off with him innawoods and Arnold covers Luna with mud and explains that Predator hates mud so much that he refused to program it into his targeting goggles.
It is at this point that Predator starts stalking around the woods blowing up trees with his arm missiles trying to find Luna, and Arnold is all like "We need to take the fight to him", so he and Luna fashion bows out of 'Nam trees, and they climb up into a really tall tree and Arnold just so happened to have a grenade or something in his pocket and he puts it on an arrow and shoots it at Predator who explodes.
Now Predator is on the ground and he's like "AHHHHHJHHH" which is basically what Predators say when they need backup, so the mother ship comes down and and ten more Predator's jump out, so Arnold is all, "Oh no I did not sign up for this" and him and Luna run up into the mountains of Colorado which are also in Equestria, and the Predators are hot on their tail.
Luckily, John Rambo is up there and he's like, "They drew first blood, we have to fight back". Then him and Arnold and Luna set up a bunch of spike traps and dig holes covered in leaves and whatever else happened in the movie Rambo, I guess they also in a cave or something and talked to the sergent on the radio.
Then the Predators come walking through and they totally don't expect all the traps to be set up in the last five minutes and one of them immediately steps on a trip wire and a rock falls on his head, then another one is like not enthusiastic about walking between two trees since there's probably a trap there, so he goes around the trees and falls in a spikey hole and tries to grab another Predator for support and ends up just dragging him in.
So three Predators are gone and the last seven are like haha there's no way they could have set up any more traps than that but immediately one of them steps on like some spring loaded spear contraption and has an unpleasant time. Now all the Predoritos are super angry and they have the flames throwers from Alien and they're just slash and burning the forest to the ground trying to smoke Luna and the rest of 'em out, and it's working.
Luna and Rambo and Schwarzenegger are just beelining through the woods trying to dodge laser bolts left and right when suddenly Robin Williams shows up in a Jeep and is like, "Gooooood morning, Vietnam!", so they all get in the Hummer and Mr. T is on the 50-cal in the back just bop bop bop bop bop which is the sound that 50-cals make when they are blasting Predators.
Now there's only one Predator left but the gun has no more ammo and the Subaru hits a rock and Luna falls off and now her and Predator are on the edge of a cliff alone.
Predator rips off his shirt and pounds on his chest all angry-like, and Luna orders a shirt off Amazon and it arrives by drone in under 30 seconds. She puts it on and immediately rips it off so she can beat her chest as well, and they both let out war cries and charge at each other.
Predator does this super awesome rocket-punch but Luna ducks under his arm at the last second and rolls behind him and does a horse kick like horses do, but Predator is too fast for that and he deflects her hooves with his wrist since we all know wrists are immune to damage. Then Predator does a spinning back kick and hits Luna in the face from behind, then he follows up with a barrage of jabs, and Luna, she's just taking a heck of a beating, but then finally she ducks down under his attacks and does a stabby-stab in Predator's chest with her horn, and Predator is all "Oh dang I have suffered mortal wounds" and Luna is looking all smug until she hears a beeping noise and realizes it's the Predator-bomb about to self destruct Vietnam.
Luckily at that second, Robin Williams and the others show up in the Mercedes, and Arnold is like, "Get to the chopper", so they're all in the jeep now and it's like the last level of Halo 3 with trees exploding everywhere and they're just going off these sick jump ramps trying to hit all the shortcuts, meanwhile the ground is collapsing as the planet implodes, and this super suspenseful orchestra music is playing in the background.
So they get to the chopper with 10 seconds left to go, and they don't even bother getting out of the Honda, Robin just jumps it off a ramp straight into the belly of the helicopter and it takes off just in time to outrun the gigantic fireball from the explosion and Princess Luna is like, "Phew, I'm sure glad we got back to the future", and they all fly off into the sunset, The End.