Spoiler: That time I accidentally trivialized what the GM intended to be an epic battle
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We were playing Pathfinder. We're a small group to begin with, normally 3 party members, and one of them had IRL issues, so it was just the two of us. We're partial gestalt, level 8//6. I, the melee guy, am a unicorn Zweihander Sentinel Empyreal Guardian Warder//Aegis. My party member is an aasimar Kineticist Psion//Tactician. The two of us are trying to overthrow a tyrannical government that's a thinly-veiled reference to Communist Russia, and our current goal is to decapitate the secret police organization.

We manage to get inside the building on false pretenses, and make our way to meeting with the heads of the secret police. But, before we are permitted in through the locked door they're on the other side of, they communicate with us through a magic mirror used for that purpose. Apparently, they've dispatched runners to look into our backgrounds. Since our story will not hold up to serious investigation, we decide "heck with it, we're close enough. We can brute-force it from here."
Looking at our resources, we've got a couple options. I know Impaling Strike, which ignores hardness, and so could probably just chop the door down, or at least cut the lock apart. Alternately, my buddy knows Breach, which is the psionic version of Knock. We go with the second one, on the basis that it's probably faster and quieter than chopping the thick wooden door open with my greatsword. The door turns out to be magically locked, but my buddy beats the caster level check and the door opens. Since I'm much tougher than he is, I take point. I walk into the room, greatsword drawn, and announce that we're going to end the secret police. The heads of the secret police, obviously, take exception to that, and open up with everything they've got.

Turns out there's six of them. One of them opens up on me with a power that we both recognize as Ego Whip. I pass my Will save.
"You know I have Stalwart, right?"
So, instead of a reduced amount of Charisma damage, I completely ignore the effect, like if I had Evasion and saved against a Fireball.
My buddy is next, and he activates a defensive power (Energy Retort) that makes it so the first time he gets hit with an attack each round, the attacker eats a 4d6 ice blast.
Next is some more enemies. After another Ego Whip utterly fails, they switch over to Reflex-half energy attacks
"You know I have Evasion too, right?"
They also discover during this time that I have Combat Reflexes (keyed off Int rather than Dex), that my reach for purposes of AoO is 10 feet, and that I can hit them on anything that isn't a natural 1.
Within 2 rounds, half of them are incapacitated or dead, and the other 3 are fleeing for their lives. Then my buddy uses a power that's basically Psionic Entangle, slowing them down. They're still trying to escape, but I'd have to move through the area.
"You know I can fly, right?"

And then it turned out that they were all level 3 psions, and the GM's expected plan was to have them spam Ego Whip at me until ultimately I fell down from that (since normally it still deals some Charisma damage even on a successful save) and then there'd be an epic battle between my buddy and however many psions I wasn't able to take down before getting worn down. Thank gods I built with the intention to survive anything anyone throws at me.