Best moments were with old Mordekaiser and old Sion funnily enough. Now when I started playing League I didn't play ranked at all, saw no point to it. So I didn't start playing ranked until I have 2.5 k normal games played. This was before I realized what MMR was so it turned out I was already playing against Plat and Diamond players and didn't even realize it. So, after a while on a whim, I go into ranked with my main, Mordekaiser. The game was cruise control easy because I was in bronze elo with Plat/Diamond level mechanics, hell I remember people asking me if this was a smurf or if I was elo boosting, I wasn't, just had so much prior experience. Anyway, I was like 14/0/XX or something stupid like that, me and my ally Graves were going down mid, doing the whole playing stupid because no way we could lose thing. Suddenly, we get jumped by all five and Graves dies immediately, at this point I have like 3 to 5 levels on everyone, and I couldn't run, so my mindset was "meph, might as well take the ADC Ashe with me." because I thought I was gonna die. I E ulti her and she dies immediately, then with my shield, my ADC ghost, and my abilities, I get a 1 vs 5 pentakill.
The other one with Sion was me getting an unofficial penta kill, was playing with friends, AD Sion, you know that champion that was dumb as all fucking shit if he could get to end game and actually touch people, I ended up cleaning up four, saw twitch mid lane and ghosted after him for the unofficial penta.