A long time ago in a basement far, far away, we were playing AD&D 2E, and the DM had mashed together the Tomb of Horrors with some homegrown elements.  There were three players and we were all doubled-up on characters to fill the ranks.

We had just gotten done with a massive combat and we were in bad shape for hit points and spells, but we managed to finish it without a single one of the PC's dropping into negative hit points.  We were riding high on our apparent success and feeling a bit cocksure.  The DM decided that our egos were getting the better of us and that we needed a little more time under the tenderizing mallet.  As a result, he selected that precise moment to drop a high-level banshee mage NPC on us that he had been planning to save for a future predicament.

Combat began promptly and, predictably, over the course of the next few rounds, the banshee laughed maniacally as she floated above our heads, out of reach of our melee weapons, and alternately wailed at us and casted high-level AoE spells into our midst.  It was miserable.

The paladin went down almost immediately as she initially focused her hatred on the already heavily-battered holy knight.  The cleric was next in line and succumbed to one of the death wails.  The fighter managed to save against a couple of fireballs and got a few good magical arrow hits in before getting juiced by a lightning bolt on a failed save.  My rogue had been sent running from fear halfway through the fight.  With two PC's left in the fight (my fighter/mage and another player's single-classed mage) the banshee had only been lightly hampered by a couple of arrows and a handful of magic missiles we still had remaining between us.  Things weren't looking good.

I spent my last magic missile on the banshee and switched to grabbing whatever magical weapons I could find off the others' corpses to try to hit her with any kind of ranged attack.  The mage was even more desperate as he didn't even have a THAC20, much less a THAC0, to hit the banshee with any magical, ranged weapon we had at hand.  However, one of the very few spells he had left happened to be Wall of Iron and he dived into the PHB to look at the spell description once more.  We were desperate.  Desperate PC's get creative.

On the next turn, the mage announced his attempt at a rectal extraction to the DM.  He wanted to cast Wall of Iron above the banshee's head and drop it on her for a coup-de-grace.  Now, of course, the DM was...skeptical, but he also liked to reward creativity, so, grabbing the PHB out of the player's hands, he perused the spell's description and began to deliberate.  After a few minutes of arguing with the player, he decided to allow an attempt, BUT he also placed some conditions for success.  First, it could only hit on a natural 20.  Second, the banshee was given a percentile chance that the wall would fail to hit her partially corporeal form.  Finally, the banshee would be afforded a save vs. death to resist the spell, despite the spell having no listed saving throw.

The mage cast his d20 with a prayer to his god.  Miraculously, a natural 20 appeared!  The wall appeared directly above her.  Now the DM allowed the player to call high/low for the percentile to phase through the wall.  The player called low and the DM cast the dice in front of his screen for us to see our fate.  3% was the result.  The wall had driven her to the ground like a giant, metal bat crushing a mosquito!  Finally, the DM rolled the save vs. death for the banshee, treating her as a level 20 mage.  The result: a 2.  She had failed.  After a quick round of healing potions, the party was saved (well, except for that cleric, but that is a story for another time).

It was the first (and last) time the DM allowed for a Wall of Iron to be used offensively, but it worked like a damn charm.  #DDBStyle

Early on in our game, our party was beset by a band of goblins. My Dragonborn Sorceror's turn comes around, I cast Chaos Bolt on the closest goblin. Roll the D20, Natural 20. The party was very happy, the DM impressed. "Roll for Damage" he says. I roll 2d8, snake eyes. I evaporate the first goblin, then the bolt jumps to another. Doubles again, and then a third time. I managed to evaporate four goblins, ending the goblin attack in one turn. And that is how my character earned the nickname "Scales the Annihilator".

I must have used all of those dices good luck in the one game though, because they've never rolled well since XD #DDBStyle

Man, that DM did you a favor (felt guilty?).  Banshee are incorporeal and can float through objects and people, they only take damage if they end their move within them and even then it's marginal damage.  Story-wise it's cool, harrowing tale.

"Incorporeal Movement. The banshee can move through other creatures and objects as if they were difficult terrain. She takes 5 (1d10) force damage if she ends her turn inside an object."

It was 2nd edition AD&D and he wanted to give us some kind of a fighting chance after nearly wiping the party, so he conjured some rules for success.

I only just discovered the game back in 1990 and a classmate was my DM. I rolled quite well and as such was able to select the rare Paladin as my class. As a god I chose Tyr (my DM gave me a choice between him, Torm, and Helm) because he was a Greater Power and thus surely the better choice.
Then when we started playing it turned out Tyr (or the DM) was quite restrictive what I could and couldn't do. I don't know what it was about but I remember having my character walk off in a fuss in a random direction. The DM decided to get me to turn around by making me meet an Ogre as a random encounter.
My first ever D20 role and I roll a nat 20! That meant the ogre got killed in one fell swoop by this grumpy paladin of mine! #DDBStyle

My Valkur-worshipping Tempest Cleric was duelling with a sahuagin (homebrewed to essentially look like a Street Shark) serving the evil sea goddess Umberlee.

After a few rounds, both were battered and bruised. With a massive chomp, the sahuagin picked Percy (the cleric) up, and attempted to swallow him, This attack took Percy to 0 hit points - with his last gasp the cleric invoked his final Wrath of the Storm ability to shock the beast, rolling the exact amount needed to kill it.

The rest of the party just saw the cleric get half swallowed before a burst of lightning exploded the sahuagin's head, leaving the Percy unconscious but still alive on the floor. He needed new armour afterwards, as the fishy smell just wouldn't come out.

#DDBStyle

I want to go deep into all the rules and background of DnD and it would be awesome !!! #DDBStyle

While playing Waterdeep: Dragon Heist we ended up in a fight with an Intellect Devourer. My half-elf rogue had already sustained a lot of damage previously, and in every round a member of the party was getting hit with significant amounts of psychic damage. When our DM called on me to make an Intelligence saving throw, I was certain I'd end up unconscious. I rolled, heart in my throat, and got over 20 with modifiers. The DM ruled that although I took no damage from an attack which should have killed me, I resisted the effects so strongly that I ended up incapacitated for the rest of the game, trapped in my own mind. It was a turning point for my character, activating latent psionic powers and causing a subclass switch to Soul Knife. #DDBStyle 

The party had finally discovered the secret entrance to the ceremonial catacombs beneath the monastery. The 4 members crept down the dark stone stairwell that laid along the back wall of the chapel secretly hidden behind the stone alter. Light could be seen at the end of the stairs leading down to where a stone archway opened up leading into the depths of the catacombs. Silently approaching the bottom of the steps the party could hear the chants of the cultists from within the chamber. The party stops in the darkness at the bottom near the entrance quietly determining their next move. The dwarf fighter makes a gesture that the high elf interprets as an impulsive and dangerous move to barge in. The wood elf rogue and ranger both grab the shoulder of the of the dwarf nodding their heads "no". The cleric points to the inner chamber where the ceremony is being held. A large stone chamber with several pillars to support the ceiling is dimly lit with small torches. In the center there appears to be a square pit where 6 cultists are standing in two rows of three, one row on each side. In front of them is a platform with an alter where a priest is chanting. On the ceiling are two more rows of cultists standing upside down in an effortless manner. The 6 cultists on the ground are holding a girl dressed in a white gown above the pit like pallbearers at a funeral. The party recognizes that this is the kidnapped girl they have been searching for. The rogue suggests a sneak attack and points a path to the platform behind the priest. The cleric and ranger agree a surprise attack on 13 unsuspecting cultists is a much better plan than barging in. The dwarf with a grumble accepts the plan. (yes; mess up one roll please.) With a solid roll and good stats the rogues first moves into the chamber are unnoticed by the cultists who appear to be entranced in the ceremony as they toss the girl from the cultists on the floor to the ones standing on the ceiling. Another solid roll and the rogue moves to the next pillar as the cultists on the ceiling drop the girl who is then caught by the 6 standing on the ground. Another successful (Seriously?) sneak maneuver moves the rogue behind the platform as the cultists on the ground again toss the girl in the air to be caught by the cultists on the ceiling.  "These guys must be really concentrating" thinks the rogue as he crouches behind the platform where the priest continues the ceremony. The cultists continue their action of tossing the girl who has now been caught again by the cultists on the ground. The air is cold in the catacombs and the cultists words are dark and chilling as he makes one more sneak maneuver to get into position. (Ok this guys dice are totally loaded or something. I mean it took y'all 2 sessions to find this almost in plain sight secret place and you stop to meet every five seconds to determine that the rogue is just going to do a sneak attack. Ok Ok I'm moving on; solid roll man.) Positioned within striking distance of the priest the rogue maneuvers to make his attack as the cultists toss the girl into the air to be caught once again by the cultists on the ceiling. (A natural 20? Are you freaking kidding me. do you roll anything below a 15? Seriously where'd you get those dice? WOW!!) With a swift attack from the darkness the rogue lunges forward thrusting his short sword into the back of the priest. (OMG the dice are with you tonight man)  With a massive thrust of his short sword he performs a critical sneak attack that pierces through the priests back and out his chest slashing his heart in the process. The priest falls down off the platform in front of you as the cultists on the ceiling release the girl into the pit while chanting "Tell no one of the ceremony. Tell no one of the offering to our god. Tell no one because no one would understand that happens here in the dark. For in the dark are you're only friends. The darkness is you're only loyalty!" The rogue watches from the platform as the girls body falls into the pit. Tumbling and turning into decayed ashes as she drops into the darkness below. Without hesitance the dwarf barges in "Baruk Khazâd!" (dude this isn't LOTR) (I don't care. LOTR is the best.)(whatever man, lets roll initiative. the sneak is over. OK the cultists attack last.) With an impressive roll the dwarf moves into position and performs a shove attack that sends a cultist flying into the dark pit. His body turns to ash as he plummits into the darkness. The ranger lets loose an arrow that pierces a cultist who's standing on the ceiling causing him to drop to the ground clutching his wound. With that observation the cleric sends out a scorching ray striking three cultist on the ceiling that sends them falling into the darkness of the devouring pit. Another sneak attack from the rogue leaves a cultists dead on the floor. (hmmm cultists suck) The cultists begin to attack the party only to find themselves lacking in their abilities to strike. (maybe its just me but I cant seem to roll anything above a 5.) The party moves in harder and clears the catacombs of the cultists. The party cheers for their conquest. Unfortunately their victory over the evil in the darkness feels lessened with the realization that the girl was not saved. (At least that's what I would have thought)(time to loot the bodies) (and search for treasure!)(wow, ok ummm, where would you like to start?)(you're just upset because we just destroyed your silly cult.)(Perhaps, but don't you worry cleric. there will be a next time....) #DDBStyle

I was running a game of Curse of Strahd. The party was being chased by Strahd through a cave. My druid dwarf turns to me and says I cast thunderclap to destroy the cave. 
He succeeds. I say make a save for falling debris, nat 1. I quickly think I am about to kill of my dwarf player lets give him one more try and see if he passes. Roles to save another nat 1.

Regardless during that heart raising moment we had a friend and hero sacrifice his life to stop strahd and allow the rest of the party to escape. #DDBStyle

We were going against Rakdos in a homebrew game. The barbarian got MCd hard and taken out of the fight taking down the wizard. The cleric was healing and reviving as quickly as possible. Then there was me, the druid that was screwing off in fire elemental form so I could swim in lava. 

Well after seeing my extreme usefulness and all the legendary resistances get used up, I just walked on up, touched Rakdos in the hope of Plane Shifting him away.

The DM rolled a 2 and a 3 to save, getting the demon shifted to the fields of celestia. Wild rides.

#DDBStyle

My best memory of a truly pulse racing set of dice rolls was in Tomb of Annihilation when we were facing Ascierak. And I, a dex based rogue/ranger named Tiffany, not only succeeded in grappling Ascierak but also succeeded in throwing him through his own sphere of annihilation and surviving only thanks to a trickster God, 2 spells, and the fact that while Ascierak passed through the Sphere I didn't. I also on the way down successfully slammed him into the wall, in total he ended up dropping to a total hp of about 20 when we finally landed on the lava. He barely failed his teleport only being 1 number off the required roll and proceeded to melt while I thanks to Water Walk, an immense amount of fire resistance, and also a trickster God having blessed me somehow survived. #ddbstyle

First Time Playing, my team had run into some Lizardfolk. Everyone else was out for the count and I had one shot to take out the final lizard before I too was knocked out, but I needed to roll as high as the dice could give me. I picked up the dice, shook it in my hand and rolled. Nat20! I defeated the final lizard and our team just managed to escape.

#DDBStyle

Just recently, playing a paladin in a Slitherswamp run through with a party of three. We were attacked by a Death Slaad and cut off by a Hydra. Attrition begins to take its toll. Just as it looks like we might not make it, double attack, double critical hit, double smite. The Slaad imploded, and we went from a likely defeat to mopping up just like that.

#DDBStyle

Every single time my wild magic sorcerer rolled on the wild magic table... Until I tpk'd the party with a fireball #DDBStyle

My heart was pumping when my wild magic sorcerer cast a spell on a frost giant and the DM just laughed at the roll on the wild magic surge table. When the giant's turn came, his club came down on my halfling and crushed him to death, only to be immediately resurrected as a dwarf for the rest of the campaign.

#DDBStyle

A while back , me and my party were playing the Waterfeep:Dragon Heist campaign and there was a iob where the party slowly ended observes a suspicious character at night for a week or two. Our Ranger was busy irl so we assigned her to the job. Once she returned, the dm gave her the information and set her loose to do as she wished with the information she had. One of the main details was the character had an unusually powerful magic item that he had with him at all times. Our ranger decided to steal the item, a greataxe, at night while he slept. To the best of my knowledge, she was a level 3 ranger and he was a level 6 fighter with a super overpowered axe. I think he would’ve 2 shot her but fortunately the dice let her live. But it was constant awaiting demise. 

PS:If the person being stolen from had dark vision, it think the ranger would’ve been dead in seconds…

#DDBStyle

It was my very first session for the very first D&D campaign I played, and I came prepared with my first character, Clyde S.R. (21-year-old male half-elf, warlock: archfey, noble), that I've already grown really attached to while making his elaborate backstory beforehand. Because of this, I was already thinking ahead of myself and multiple scenarios and what ifs were already playing on my mind about the cool adventures and plot twists he would experience in the campaign. During the first session of that campaign, nearing the end of the session, my character was suddenly all alone and faced with a near-death experience in the hands of a couple of quasits without any backup or anyone to help him out. After trying to defeat 3 quasits alone successfully, he was left in a do-or-die death match with the last quasit with only little health remaining for both. Eventually, the quasit managed to deal a blow that knocked Clyde unconscious but not after he dealt the killing blow to the quasit leaving both to die in the middle of nowhere. I had to roll death saving throws at that moment and was so scared that it took me a minute before rolling my first death save. I got 2 successes in the first two rolls but suddenly on my third roll I got a critical fail (1) meaning that I now have 2 successes and 2 fails. That was the moment everyone gasped, and I screamed. Everyone was panicking for me, and I was scared shitless to lose this character that I've loved already even at the first session of our campaign. It took me about 10 minutes before I could even roll the last death save that will determine my character's fate in the campaign. When I finally rolled the last death save, my dice fell of the table and rolled away on the floor, and everyone was just silent. No one wanted to look at the dice on the floor as everyone was also anxious, so our DM decided to go towards the rolled d20 on the floor and showed us that he took a picture before touching the dice for proof. To our surprise, I rolled a natural 20 as my last death save, and everyone was just screaming in joy and relief. My hands were numb and shaking during those times and I felt so happy that those rolls save my character, Clyde. Fastforward to a year after that, we finally finished the campaign and my character Clyde reached level 20, is now a demi-god and chosen of the Sun God, Amaunator, and a young king to his reclaimed forgotten kingdom at 21 years old. #DDBStyle

This happened many years ago. I was playing DnD with a bunch of friends and we take turns being the DM between campaigns. Everyone at the table has experience at both being a DM and being a player, and we often do short debriefs after particularly good/bad encounters. So we started this new campaign and we agreed in advance that there will be no fudging of dice and hp one way or the other. All dice rolls are done in the open and the DM will play the enemies with intent to kill. We also used a d100 table of extra things to take effect on a crit.

We were about halfway through the campaign when we ran into what is basically the mid-boss of the campaign, an Ogre Mage and her goons. After a tough fight, our party was in horrible shape, the paladin and ranger were both down with one failed death saving throw, our cleric was down with two failed death saving throws and our sorcerer was stabilised but unconscious and out of the fight. Our last man sitting was our bard, who had both legs broken by an ogre's crit earlier in the battle, he was also right on top of a wall of fire so he's most likely dead at the end of his turn. The bard had one healing potion and no spells left, so we were mentally prepared for a TPK. The bard decided that rather than drinking the potion and prolonging the TPK by only one more round, he will throw one last vicious mockery and go down fighting. The Ogre Mage failed her save, the bard rolled 2d4 and got a 7 and the Ogre Mage dropped dead. The DM told us afterwards the Ogre Mage had exactly 7 hit points left and what would have been a TPK ended being a very slim victory. #DDBStyle

We were playing in a homebrew campaign, rolling Dexterity checks to control a ship through jagged rocks that was exponentially increasing speed threw an underground rapid, when suddenly a light appears on the horizon.  As we por out of the light, our ship freefalls down a waterfall, plummeting several hundred feet.  As a warlock, I cast spells saving several members, only to roll a Natural 1 to grab sail to parachute down...hitting the ground and insta killing my character.  Worth it.  #ddbstyle