It was an original D&D tourney at a convention in Houston, in 1976. The dungeon designers wanted to include a completely unbeatable monster, to test if people would flee when necessary. So in a 10x20 room, they had a 134-headed hydra. (No that is not a typo. This monster had 134 separate attacks.

We opened the door. The DM described the monster. We closed the door. (We had a very organized party.) At a minute's planning, this occurred.

Fighter: I open the door.
Magic-User1: I cast Web.
Thief: I toss a flask of oil.
Cleric: I throw a flask of oil.
Magic-User2: I throw in a torch.
Fighter: I close the door.

DM: Hmmm.. 1d6 damage to each head. (rolls a 4.)

Fighter: We wait two minutes. I open the door.
Magic-User2: I cast Web.
Thief: I toss a flask of oil.
Cleric: I throw a flask of oil.
Magic-User1: I throw in a torch.
Fighter: I close the door.

DM: (rolls a 3) All the heads are dead. But ... that monster was supposed to be unbeatable!
Thief: Sorry. We loot the room.

So - two 2nd level spells, a few standard supplies, and the 134-hd monster is dead. The plaque for winning that tournament is hanging on my gameroom wall.

[The next year, they had a 134-headed flameproof hydra. We ran.]

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In 1979, we're running the tourney - only now it's the new, exciting AD&D. (In fact, the prize was a copy of the new DM Guide, signed by Gygax.)

It was an adventure set in Japan. At one point the party enters a large cavern and sees a Gold Dragon 70 feet up, in full stoop. One party said, "I cast Dispel Magic, and we duck back into the tunnel."

DM: "What for? Dispel Magic doesn't work on dragon breath."

Player: "Look at the Monster Manual. Gold Dragons have no wings."

By the 1E MM, it was true. The dragon fell to its death, and the party nonchalantly strolled in to claim the treasure.