Tony from series 2 when he walked into a room and he was trapped. Mogdread then appeared. Along with the background music as Tony perished was scary!

Was that the one where he couldn't get past the catacomb bite and walked through the wrong door, only to be greeted by Moghdred saying "You've walked into one of my play pens, play a while, play FORVER!!!!!" (Maniacal laugh) The acting from the guy who played Moghdred was 10 out of 10!

The one for me was when the Oracle of Confusion first appeared. Watching that at 10:45pm the other week was pretty creepy even now

Also did the Oracle of Confusion only appear once?

I saw that on Challenge a few weeks ago for the first time and thought that was as creepy as anything. That would have freaked me out as a kid for sure.

Akash's advisors from series 2 were hopeless

Also there was another team from series 1 or 2 that got to the room where you had two sets of spears coming from the right/left and you had to time it and avoid them. The team spent about a minute going "Go!!! No Stop!!!! No No Go!!! Stop!!!!! Now Go!!! Wait Stop!!!!"

Eventually they made it through but I remember thinking that would have driven me mad

Regarding the original post the swinging pendulum room indeed only appeared once. The room with the green monster made several appearances, once when Cedric attacked it.

Mildred appearing as Treguard and attempting to goad the dungeoneer into the cooking pot. Treguard was put under a spell but the team avoided the trap.

Cedric killing a dungeoneer

The Medusa room and the dungeoneer/team turning to stone

One team failing to take a guiding rod and trapping themselves because each exit lead back to the room they were in

I can only remember the giant making one appearance (not to be confused with the giant troll)

Gretel being trapped by Ariadne?

A team dying because of darkness (first ever quest)

Moghdred posing as Cedric

Mildred killing one dungeoneer by leading them into a bomb room due to them previously taking the wrong object

I don't know if anyone remembers a death in series 2 when a team fail to take the gauntlets and therefore can't deal with a catacomb bite. They go into a room to the left where Moghdred says "You've wandered into one of my little play-pens, play a while, play forever! (evil maniacal laugh and dungeoneer dies)

Just before that though is when they meet the oracle of confusion in the object room (the one with the stairs at the top) who clearly says "The way forward is the way back" but the team don't go back. This isn't mentioned concerning the death weirdly.

There's also a random one in series 2, where the dungeoneer wanders into the object room at the top of the stairs, and this ghostly shroud floats over and kills them. I never understood that one

There was a good one early in series 2, where a guy failed to pick up a shield in level 3. A few rooms later he came up against a Medusa which turned him and his team into stone.

Treguard then says "Oh dear, I think all I'm going to get from them is a stoney silence". It was the way he said it, I was laughing for ages after that.