"Oh god what is that!"

[Twichyboy]

I've had a few of these moments with my PC's, I guess its because i really enjoy throwing seemingly impossible targets at them for fun

Probably the best one was Spelljammer when the PC's were level 4, or 3 i can't really remember they were hired by a Dwarven Scavanger's guild to help clear out a Goblin War Station. the PC's docked at the empty station and began looting, not noticing at all that the station was completely abandoned

Until they say the Dwarven Transport fleeing and the two corsair ships with it horridly destroyed, then they noticed that their group of 5 lvl 3 or 4 chars had stumbled into a Elder Black Dragons Lair. after about an hour of plan discussion they finally were able to out maneuver the black dragon, get on their ship and actually KILL the dragon by ramming it three times.

Tonight the PC's at lvl 6 are going to meet the BBEG in the campaign which is a Giant Ogreish Mindflayer Demigod, i'll edit this post after i see their horrified faces

 

[Holy Bovine]

Perhaps it's perfect timing. Maybe it's the surprising reskin. The most unexpected moment. Or the too-high level thing showing up way too soon.

Whatever creates it, its the appearance of a monster that makes the players react with surprise, horror, amusement, and excitement all at once. They tell this story with smiles, because it is an event that stays with them.

What are yours? What's that one monster, in that one situation, that got the best reaction?

Oh I remember this one! In a Age of Worms campaign set in the Scarred Lands (Hollowfaust to be precise) under 3E the PCs were getting surrounded by multiple Sons of Kyuss when the cleric decided to make his move. The PCs were in a bad way the player, obviously feeling the tension of the situation (I think half the group of 6 were unconscious), proudly turned the undead and yelled "F%%K BACK!!!" (Sorry for the crude language). He meant to say "Get the **** back!" but was so rattled and nervous he just blurted that out! The best part was the player himself was a very calm, cool sort of dude who never got rattled by anything and almost never swore. "**** back" became the battlecry not only of the cleric but the party was well.

 

[shipratstew]

I have few times my players have asked "what the hell?" But my favorite time was when they cobalt pieced together what one of my NPCs was.

Long story short time. The group was a bunch of neutral to evil types with one lone honor bound LG fighter. They come to a town that is under attack by some demons and they squash "forget the towns folks, let's loot." This worked for me as they started to go house by house looting and fighting unfilled they come to the local watchhouse/jail. When they enter they find a man who won't stop grinning and is just staring out the bars. Now this was just a toss away NPC who I thought they were gonna leave to the demons but the party's evil cleric takes notice of home and insists that the group free him. At this point I asked for perception checks and everyone fails but I still give then a hint, "while his eyes are on you, you feel like you can't cast spells." Despite this they bring the guy with them.

Fast forward 6 months of real time and almost 20 sessions and over this time they have seen all of their magical equipment lose its magic. Multiple people on the team have seen this guy's skin moving as if something is crawling underneath it. All this time and me dropping mad hints and still no connection drawn to this creepy and by this time proven murderer they have following them around.

In the end the party's fighter gets fed up with losing his items and he confronts the smiling man. Rolling 4 nat 20's for one attack the fighter kills the man and rips off what he correctly thought was a mask revealing the small beholder that had been grafted onto a humqn body.

As a side note the fighter got all new and better gear soon afterwards.

 

[nai_cha]

As a DM: I described an object mimic as something like, "You see a large chest covered in fine leather. The workmanship is obviously of very high quality. Stamped all over it are designs of a fleur-de-lis and the initials (something something, an important dude in the game)."

The players went, "AHHHH OMG A LOUIS VUITTON STEAMER TRUNK (yeah, totally out of character but whatevs) LET'S OPEN IT NOW."

Me: "Roll initiative."

As a player: Our entire party was put through a series of "trials" to test our purity of heart and commitment- they were really hard encounters! No time for extended rests or anything.

Then when we emerged victorious, we were taken back to get judgement passed down on us...and eight dragons, each described as big and majestic and really effin' scary, rise up from the ground. Roll initiative!

 

[jonesy]

This was a decade ago:

The party had been hired to remove a worm infestation at this vast plantation. They arrive very late in the evening. The sky is dark, rain is pouring down, and they discover the wet ground filled with tiny dark blue earthworms. They start squashing them. Then they notice that the worms seem to be coming from an old mine. As they get closer to the mine entrance and the mountain that is shielding it they realize that the worms coming out of the entrance are getting slightly larger the further in they get. They fight their way slowly downwards into the tunnels, which are a glimmering pink. The floor has pools of corrosive slime where the increasingly large worms wallow. Finally, far within, they discover a cult of crazy orcs who are worshipping a worm idol. The leader of the cult has a pair of large Purple Worms that he fights with. In the ensuing battle one of the PC's is killed, and another has to be carried out. They get back up to the mine entrance where one of the PC's makes the suggestion that they should block it, just to be sure. The wizard gets the idea to crash part of the mountain on top of it.

Just then, the sun begins to climb up. The rain ends. And they notice the mountain is kind of purple. And it's moving.

And so is the 'mine entrance' they just came out of. And it's lined with teeth.

The wizard goes: "YYYYYYYÄÄÄÄÄÄÄÄKKh!!!!"

 

[RangerWickett]

Well, there was the beholder hiding inside a prismatic sphere that moved with him. That one was popular for how horrible it was. (And the fact that the PC who had the spell to knock out the first layer was trapped outside the battle behind a giant sphincter.)

Oh, and I stole the blood fox from either Piratecat or Sagiro. Basically a tasmanian devil that burrowed into people's torsos.

But maybe the best was my first 3e game, when a party of 1st level PCs came upon a group of cultists summoning a demon. A 10-ft. tall, skeletal demon that cursed everything it touched. It set a nice tone of "stabbing won't always work."

(They ended up killing it with rope.)

 

[Twowolves]

In my old Scarred Lands game, I had an NPC contact get mauled publicly (by the fountain of the city's main plaza, albeit at night) by an ivisible stalker with the far realm spawn and mist creature templates.

Something invisible and (unseeable with magic) made of mist with dozens of tentacles ripping apart and exsanguinating a dwarf 30' up in the air, all to make off with a magical astrolabe. Not as awesome as some of the stories in this thread, but a favored memory of mine nonetheless.

 

[Traveon Wyvernspur]

Would this qualify for your "Oh god, what is that"?

I was running a campaign through Ravenloft for the first time back in 2E and one of my players made a gypsy mad and she cursed him with the lycanthropy curse, but he didn't know it until after the next full moon... He was out adventuring and set up camp for the night in the forest, he then went to bed, soon after that the full moon came out from behind the clouds and I skipped ahead to the next morning and him waking up. He was in a small shack, naked, and covered in blood and gore. All around him were body parts of a teenage girl he had torn apart in his werewolf form. I got a good reaction out of the player when his eyes went wide at my gory description of the scene and it was definitely a WTF moment for him and he was the "what is that?" until he was able to find the gypsy who cursed him and appease her to remove it. Fun times.

 

[was]

Carnivorous butterflies

 

[Traveon Wyvernspur]

Carnivorous butterflies

I for one would love to hear the story behind it, sounds like it was interesting.