A while back, when I was first getting back into D&D, I had joined a group on discord about a pirate themed campaign with a mix of divinity, there were 5 of us total in the campaign including the DM. There was a monk tiefling named Valgrim who's fists were to be feared, my yuan ti impure( a mindflayer disgussed) named Nox who was thought to be the weakest, a asimar palidin named Abyssl, and two others who i can't remember the names of right now.
Some backstory, the party had travled to an island hosting a carnival in hopes of finding out why a strange plague seemed to have started there, but nothing really seemed out of the ordinary. While exploring the carnival, Valgrim had partaken in a collesium fight against the company's champion and won in a spectacular fashion. The company however was mad that he won and was going to try and force him to be their new champion to keep raking in money. However Nox was not having it and being a sneaky wizard, he made a proposal, he would fight against the 2 strongest members that worked for the company, which turned out to be the manager's bodyguards, two harlequins. The entire party was confused on why I even offered this thinking nox was the weakest by far and only being the brains. But one think they forgot is that brains almost always beat brawns.
I the player had a grin on my face as we rolled initiative in the collesieum, and went first (glad they rolled poorly). My first and only action was to cast the mind flayer's mind blast attack and have them roll a saving throw, which they failed misserably with like a 2 or 3. The dm was rather surprised, forgetting that he agreed to let my character be a mindflayer who's int. was much higher than anyones especially these guards. Even with his surprise however was when the dm described how the two dropped to their knees, clutching their heads in pure pain and agony, saying they had began to cry blood do to their failed rolsl compared to my roll in damage. This got every member of the party to be scared of me with Abyssl's player asking how I could do that. All I answered was with "never anger nox". We later had Nox reveal he was a mindflayer who was diguissed and was only working with the party to find someone who was screwing with the mind flayer's children and was forcing others into servitude.
TLDR: A corrupt company got mad that their champion lost to a nobody and tied to take him. got tricked into fighting a mindlayer and two guards went insane.