Your biggest screw-up as a DM?

[Mouseferatu]

I don't know if I'd call this my biggest screw-up, since it was a fairly minor detail, but...

Me (DM): The corridor finally ends in a T-intersection.
Party: We'll go left.
Me: So you're going towards the secret door... (pause for laughter and incredulous looks) Oh, crap...

 

[Thornir Alekeg]

Along the lines of forgetting SR and things, I ran an encounter with a Blade Beast from the Creature Collection. This creature absorbs bladed weapons into itself when struck by one. I completely forgot this the first round of attacks and by the time I remembered, it had already been hit by two bladed weapons. It ruined a lot of the "Oh S !" factor of the encounter since it was killed the next round.

 

[MDSnowman]

Well aside from the stands forgettign spell resistence and spell-like abilities (which I get over now by studying monster write ups closely and planning out their first couple of rounds of combat) most of my mistakes have historically been in picking up players.

I had a very interesting post-modern idea for a Warcraft RPG game, recruited six players and watched as the game fell apart around me. I'd managed to find one or two decent players and four or five hack happy power gamers who didn't even understand the concept behind the game with a diagram.

My recent Mutants and Masterminds game has seemed to suffer none of this I have five players who all seem to be on the same page as I am.

 

[Sarellion]

My biggest fumble was in a GURPS game. It was Sci-Fi and our Troop went against some Mechs. I designed some kind of LRM -20 with 6 pound missiles, never checking the actual numbers of damage.

One hit killed their vehicle and the whole crew

 

[UltimaGabe]

One screw-up I do quite commonly when DMing is referring to bad guys by their classes.

"...You come around the corner, and see a dark-clothed, half-elven rogue in a- dang it."

 

[EvilGM]

Some of a friend's mistakes...

- roll a Sense Motive check on the door (he will never live this one down)
- mispronouncing Carnivorous Apes to be Cavernous Apes... we were like why do the apes have big holes in them?
- "knowing" the rules but not as the PHB,etc say they are
- throwing in encounters 10 levels higher than the party and then dumbing them down to the point where there is no risk
- letting me play in his games

 

[Gundark]

I was running a Rifts(gag ) game and the PCs were to overthrow this evil baron. So the players excitedly start discussing ways to obtain this goal...then I said something along the lines of "OH...you notice a large window in his stronghold that you can fly thru..." The group rather disappointedly were like "oh....okay...I guess we'll just fly up and kill him...." I wrecked this great oportunity for roleplaying and to create a memorable session and instead did this chessy comabt.

 

[Maliki]

Back in second edtion I was running a group of five or six 1st level characters through a kobold lair when the party ran into several wild boars the kobolds kept as guards, the party retreated into a 5' wide hall(so the boars couldn't all attack at once). The first boar charged down the hallway and killed PC #1, the #2 and so on, as the party realized that they also could only attack one at a time. The boar managed to roll though the entire party. Four of these players were new to me and I had just met them that night. So after the TPK they agreed to come back next week, and everyone left. While wondering how the one boar mangaged to destroy the whole party I looked at the dice I had been rolling for damaged and noticed that for the entire battle I had rolled 3d6 for damage rather than the 3d4 the boar should have got, OOOPS. I never told the players when they came back the next week.

 

[Len]

One screw-up I do quite commonly when DMing is referring to bad guys by their classes.

"...You come around the corner, and see a dark-clothed, half-elven rogue in a- dang it."

That's not so bad, because by the time you finish describing the "half-elf in a dark cloak holding a dagger" they realize he's a rogue.

Now, if he was supposed to be hiding and you forgot to roll spot checks, that's a screw-up.

 

[MarauderX]

I have been tugging the PC's chains on how much gold they have and where they can spend it for nearly the whole game now, and as things are starting to get to a dramatic stance as far as good vs. good and if the PCs want to spend their hard-earned cash to 'do the right thing' when one of the players walked out. (BTW, we need another player...) I know they don't realize some of the spots where other opportunities lay for treasure that were skipped in the name of safety, but that's when I realized I had gone nearly too far. Too bad he didn't stick around, as at the end of the session they were rewarded again to make up for what they had spent. Guess it was a bit too much of the "The DM screwed us! %&$#@ Rat Bastard!!" Ah well, there's plenty more out there for the others as the adventure comes to an 'end'...