For me, there is probably four that stand out.
First is my first mafia game at BHP, which was a properly epic CYOR game in which I played as the KILLER MINE LAYER, in which I broke the game by forming a protection ring with Allie29 and was armed with daykills by Retaliation to boot. Together we were an unstoppable town army, for good and bad.
I killed a scum!pzeper just out of the blue the moment it was revealed I had a gun, and later killed a town!Chaos_Knight because of some bad reasoning. Also only ever killed town with my mines. The game was huge and had a ton of things happen in it. Jeod was scum Dr. Robotnik, I remember that. Also remember M1Garand8 was scum. And town won.
A later BHP game I remember is the embarrassing time I lost in a 3-person LYLO with scum!Allie29 and a town player that I don't remember, I think I only saw once. The loss was embarassing because I carried out a vote test with Allie29, I caught him in the trap, and then let him get away with it.
Back then most games had majority-vote hammer rather than timed hammer. So with 3 people, the first town player to vote wrong effectively ended the game. I decided to test Allie29 by voting, watching him come in to the thread, unvoted as he came in, and sure enough he voted. If you posted quick enough right after yourself, new posts were just appended to the end of the last one, so he wouldn't see the unvote. I wanted to see if he would prematurely celebrate his victory by jumping on my vote. He did vote, as the trap was intended to provoke, but he didn't celebrate. He kept up appearances as I poked at him for a response after. So despite falling in to my trap, he actually convinced me he was town anyway. And then I lost the game for town.
Third is a game that was played on another board that Westy was hosting. I mentioned this one during the last game. During the course of this game, I literally saved the day for town.
The role I was given was a one-time use ability to set the time limit for the next day phase to 24 hours. Seemed like a bad role to have as town, figured I'd never use it. Later a town player got lynched, whose role would cause the next day phase to be skipped, so there would be two night phases in a row. I petitioned that since my role said to set the next day phase to 24 hours, instead of just reducing the time to 24, that I should be allowed to extend the day phase from 0 to 24 hours. Westy told me he didn't design the role to work that way, but he liked the ingenuity of it and allowed it. So literally saved the day.
Also during this game, Allie29 (boy he sure shows up alot in these, I miss playing with him) and I were certain that the other was scum and were attacking each other hard. Somehow we both came to an agreement that someone else was scum, so we both voted that person while still sizing each other up. The person we voted for was lynched, and was the last mafia, but Westy decided troll us and made a pretend night post as if the game was still going. I don't remember how long he kept up the charade, but it was long enough for us all to collectively flip shit, I remember that.
Last is the Death Note Mafia game, and the battle with OrangeP47 during his first game.
I still remember the intense amount of work I had to do to catch him as a Kira (scum in that game) and also convince the rest that he was scum, made harder because I was also technically a Kira and everyone already knew it. I wasn't part of town, but I was working in their interest the whole time. The whole "reveal of the plan" from Orange and KY was pretty epic as well.
While in the end I think I think the game wasn't designed very well and only the various Kiras were capable of winning, I still view that game as a pretty epic showdown.