Dungeons & Dragons (animation)/Nightmare Fuel

An episode where the villain caused interdimensional portals to appear under kids' beds and his minions dragged them through to perform slave labor for him -- complete with terrified parents trying to keep their kid from disappearing through the rift. On the other hand, when Bobby, the youngest of the featured characters, is snatched, the other kids and their new ally force the portal open and dive in after the kidnapper with a determined look that promises a world of hurt for anyone who tries to stand in their way.
One of the characters got turned into a bogbeast.
- Eric must've failed his saving throw against Polymorph!
- This was 1e--there were a lot of things that could horribly alter or kill you with no save at all. Oh, wait, that doesn't help...
The fun moment in "Quest of the Skeleton Warrior" when Hank's entire outer meat layer starts to melt off.
Right here around 3:00! Maximum fun!
The kids once accidentally summoned Venger's master, which manifests as the top half of a giant green face with slit-pupil eyes above the cloud layer, and as a cyclone of absolute hellfire from there to the ground. Might not look so threatening in a cartoon, but imagine seeing something like that yourself and doing anything other than crapping your pants and curling up into a whimpering ball. Now imagine that it's following you, and can appear anywhere in the world within seconds, and you've got a taste of what Dungeon Master and the kids went through.