Yeah. So, I played with a group of four. Two of which couldn't play that night, so it was just two. Both level 3. One Eldridge Knight, the other a Paladin.
They stumbled upon him by accident. Just walked into the tower, opened the door, and hey look, a green dragon is staring at them.
Well, the EK's backstory was he was raised by dragon hunters. So what does he do? He charges the dragon.
Commence the most number of times I, as a DM failed my rolls.
Literally, the dragon couldn't hit them. Well, he did hit the Paladin once, but it didn't kill him. They managed, just the two of them, through a series of incredible rolls, to get half his life down. So the dragon starts climbing the inside of the tower to get to the outside.
The EK was having none of it. He sprinted up the stairs on the tower, and I let him get to the top the same time the dragon did.
He said "I want to leap in the air and stab him in the eye, and hold on."
"Do an attack roll, but if you miss, you're fallin gall the way down and likely dying."
He rolled a 19.
So, he stuck the sword in the dragon's eye. The dragon screams, and jumps out of the tower, with him on board. He was an EK, so he can't be disarmed, so I interpreted that as he couldn't be forced to let go of his sword, so he was literally latched on to the dragon's head. He proceeded to use his other sword to hack at the dragon, while the dragon tried to shake him off and couldn't.
Then he crits, and the dragon dies, in mid air.
"Ok, he's dead. How do you kill him?"
"I pull out my sword, and then take both my swords, cross them and scissor the dragon's head off!"
"Sweet, his head flies off. Now you're falling through the air. Make a dex save."
"19!"
"Frick. You surf the dragon down through the air, it crashes and you just stand on top of it like Legolas, and when it comes to a stop, you jump down, the dragon dead behind you. You also land in front of a house, and a man (The dragon cultists in this area) walk out, amazed that you killed the dragon they had been trying to befriend. Their leader isn't happy."
"I try to intimidate them into running away!"
"Roll that with advantage, this is awesome."
I left out a little, but that was the gist. I swear, the only thing I did to help them was I didn't have the dragon use its breath attack. Cause, you know, that would have ended the fight immediately. I figured the dragon wouldn't want to melt its treasure horde.