The, "If a single thing goes wrong this fight, it might be a little challenging" line got me good. XD

To be fair using magic missile to figure out which copy is real is very clever problem solving

The thing my players did that made me quit DMing was the feeling of them not taking the game seriously. Tired of prepping for a session every week and then getting the feeling that my players are barely paying attention.

The polearm master and sentinel interaction has always seemed cheap, but keeping enemies from getting close enough to hit you is basically the whole point of polearms.

The Magic Missile hard counter is absolutely spectacular. As a DM I would be ecstatic of a player completely broke my encounter with a big brain play like this. I would describe the BBEG panicking, struggling to think of something else, etc. Flawless.

Oh no, what did I do?

Last week: "OK, you notice that you can only see the invisible creature when your Darkvision is on; so when it passes into the light it flickers away." This week: "You come upon the creature in a room filled with torches. It sneers and disappears, so you don't have a line of sight or target." Players: "Welp. we're done. There's nothing we can do." Me again: "The room's filled with TORCHES. Well-lit, brightly burning TORCHES." Them: "Yeah, we heard you. There's nothing we can do."

I don't see why you'd be mad about the magic missiles, that's sounded really cool! Like, an actual thoughtful and strategic response!

”Guys, we gotta do something! If a single negative thing happens to us during this fight, it MIGHT be a little CHALLENGING!”

The Sentinal/Polearm Master player: “If you think thats bad, wait until I become a level 18 Cavalier Fighter, then I can make an opportunity attack on every turn”

DM:

"I'm gonna cast magic missile at second level and target each copy with a different missile" that "huh" afterwards. As a forever DM, I felt that "huh" in my bones

"Guys we gotta do something. If a SINGLE negative thing happens to us during this fight, it might be a little challenging!"

In one campaign the DM prepared a whole section where we would riddle with a SPHYNX. We were supposed to ask it one question it didn’t know the answer to in order to cross a bridge. If it knew we would take permanent psychic damage so we were supposed to think about it for a long time. I immediately said, “Yo, SPHYNX, what’s my name?”

Also, can I just say I absolutely love the comedic timing and delivery of "Thump this Beholder 'til it's atomized," and the other player saying "Done," and dropping a comically large pile of dice onto the table.

That first scenario

3:20

The "snakes" bit really reminds me of a pretty hilarious way we broke a scenario our DM had set up in one of our games. There was a sort of magic throne that would allow us to see through our antagonist's eyes and spy on whatever he was up to... but sitting on it would summon a troll in the nearby antechamber, blocking our escape. We were pretty low level, so this was a big deal. Of course like idiots we use the chair a second time, and sure enough, now there are two trolls. After pondering for a moment, we started sitting and standing on the throne as rapidly as possible, just absolutely doing an aerobics routine on it. After a couple of minutes of this, we opened the door to the antechamber and were greeted by what we referred to as "troll jelly." Turns out only so many trolls can fit in a small room before things get a little bit tight.

DM: "here's this diary, only your character has read it so perhaps you should discuss the content with the party" Player:"ok let me put it into my bag for it never to be discussed again".

"The usurper is no pushover though, as his many years as a rogue have made him very nimble. He sprints 90 feet towards you this turn, and you realize it will not be long before he catches up to you and-"