So this was my first DnD campaign, it was also the first campaign for at least one of our members. I can't remember if we were 3 of 4 at the time, to be honest, it doesn't matter. The story is not about the PCs but 2 NPCs who ended up very differently than our DM intended.
This all happened in a homebrewed world by our DM. I was playing a stern and strict monk. Not the peaceful kind, but someone who saw himself as a weapon and despised people who solved problems with anything but their skills honed through years of training.
We were in the starting town. We had just gotten back from our first quest to deal with some kobolds that had taken over a farm in the outskirts of town. After we accepted a halfling (who's name I can't remeber)approached us. He seemed to be an engineer of sorts. He asked to go to his house not far from where we were headed to clear it from kobolds too. It was nearby and paying well so we accepted his request. We cleared the kobolds in the farm we marched towards the halfling's farm. On our way there our druid started to get worried. "There should be a forest here" she said with a worried look on her face. The entire area had been cutdown, where a bountiful forest once stood now lies a barren land. The closer we got to the halfling's home the more common the scenery was. Once we got there we were surprised to see not kobolds, but one eyed robotic creatures mindlessly chopping down trees and carrying the wood into the halfling's home. They ignored us as we walked in and dispatched of a few kobolds. Soon after we found an orc, he seemed to be leading the operation. We fought hard, our first real test of might and cunning. The orc was a spellcaster but could defend himself adecuately on hand to hand combat. It was a tough fight, but we were on our way to defeat him. Unfortunately, we were low on resources and the BBEG escaped. We were frustrated, but after some investigation we found a portal in a secret chamber through which the machine creatures were coming and shut it down. We managed to track the BBEG until we reached the edge of the cursed forest that divides the kingdom of man from the orchish empire. We had to prepare if we were to head into such a place, so we turned back and headed back to town. My character was angry the BBEG got away and the druid was devastated by the mass deforestation, so we decided to confront the halfling. "Fine, I will tell you the truth, just don't punch me. I was contacted by the orc, he said he could help me open a portal to a world of mechanical creatures. I wanted to help the people of the town. There was never enough people to work the land so I thought I could automate the process." He said with a look of regret and shame on his face. "But he used me. Now the machines do his bidding and if I tell anyone that I helped an orc in his evil plan I would be sent to jail or executed". At this point our party wasn't all that happy with the halfling and most of us weren't very forgiving. We decided to call the guards and explained what he had done. He was arrested and sent to the capital city to be judged.
Two weeks passed and the BBEG escaped our grasp once more, but at least we managed to take out his ally and lover, the leader of a colony of drow. After talking with the mayor of the town and the head of the local guard we decided to head to the capital and report to the King and Queen. After a weeks journey we arrived at the capital city and explained our findings to his highness. We still had some time to kill and the townsfolk we had worked with didn't have that much to pay so there wasn't much we could buy, so we decided to go check on the halfling at the local provisionary prison. It was a small building with a handful of cells and, to our surprise, a big hole in the wall in the cell where our nemesis was suposed to be. We furiously questioned the guard. "L-l-l-last w-week, I closed my e-eyes for sec-c-cond and the wall there was g-gone." He said stumbling over his words at the sight of a furious band of adventurers. "W-we think t-t-the t-thieves guild-d was beh-h-hind it". We began investigating said guild. It didn't take long to figure out their base was somewhere in the sewers. After exploring the foul-smelling tunnels we heard people talking. It seemed like some sort of meeting, and one of the voices was from our little old friend the halfling. "See this gizmo? and this one? I can make all of these and more, but in order for me to provide you with my goods I must be ensured a place this alliance of yours". The halfling was talking with the leaders of the thieves guild, the ratmen clan and the ghoul necromancer, the local pests that plagued the capital city. We listened for a bit but our lack of patience pushed us to walk into the scene. "We come here for the halfling. If you hand him over you can keep his stuff and money." The leaders looked at each other. They would rather hand him over than having to protect the halfling from us constantly. The ghoul, who had been staring at our… female… healer, even decided to help. The halfling did not go down without a fight though, and ended up dying at our hands. We informed the King and Queen of the whereabouts of their missing prisoner and told them that a ghoul helped us with the feat. Kuul the ghoul (yup, that was his name) was thankful and we quickly became friends.
Half a year later we returned to the city, we even brought Kuul gifts from our journey. We heard that a plague had been taking the lives of the folk in the city but that a misterious man had been helping the ones who perished. Once we got there we found that 1/3 of the population were undead. Not mindless, not hungry for brains or attacking civilians, but simply going about their lives and chatting with the living as if it were nothing strange. Apparently one of the first people to die to the plague was the princess, and in their desperation the King and Queen turned to the ghoul necromancer we praised months back. They asked him to raise the ones that died as undead with free will and he gladly accepted, afterall, he had never been treated so kindly. And thus, his business began. He would raise the dead for a fee and with that money he would buy a bar where both living and undead could sit down, relax and have some good old fun.
Sadly, due to scheduling issues the campaign had to end. But the DM let us know that the halfling had been resurrected months ago by his lover and that they had gone full evil and were planning on getting their revenge on us. To be fair, we kinda screwd him over. The DM told us he was supposed to be ally we could go to if we ever needed any gadget or device in our adventures, but he quickly became our nemesis.