The hydra chase. This was earlier in my DM days, I had a party with a barbarian, and a fighter I think, they were tasked to go to a old cave to save a lost man from town, they got to the cave and navigated through some traps and some cult members. They went down a hall and found a massive solid steel door, they couldn’t break it down or pick the lock they needed a key, so they go through some more rooms and find the chief baddy: a mindflayer. To my astonishment, they both critted on their attacks and demolished the mind flayer ( ? DM nightmare cause it was supposed to last way longer) and they find the key on him, they go back to the door and on the way they see the man in a locked cell and he’s screaming that they need to leave now before they bring back the beast, in classic D&D form they suddenly hear an earth shattering roar, and the cave starts to shake. They make it out as quickly as they can and the man gets to one of their horses first and tries to leave, the barbarian threw him off and got on and as they get on their horses and Sprint out, the cave collapses and a hydra comes out of the ruins and chases the players. I had them roll athletics checks vs the hydra to see how fast they were going, It was very close at some points, almost one tick away from swinging distance and one player had said “I will do anything to get myself out of this right now” so a demon appeared and offered him shelter for his soul, he accepted. The other player found a mountain and stone shifted into the mountain, the hydra then rained terror on all the nearby towns.
The demon took the fighter to his Lord, the god of war and anger Mespidosh. Mespidosh instructed to prove his loyalty, to slaughter a village of innocents during a sun festival and to betray his friend the barbarian. The fighter left, and then he and a group of three other baddies went and destroyed a village of gnomes during a festival, the village folk remaining secured themselves in the church behind a barrier against evil, but it didn’t last forever. And once it fell they were taken as well. The fighter made his way back to the barbarian and original company, and they followed the hydras destruction. Eventually coming upon the town that the fighter had destroyed, the barbarian and others looked through the carnage horrified, blood and body parts scattered. They continued on and when they were almost upon the hydra, their cleric got one shotted through the throat in an ambush set up by the fighter, everyone was killed, the original party, the evil NPC’s and then the barbarian got out a narrow victory over the fighter. Top 10 Worst anime betrayals lol.