The Pyramid of Darkness: Part 1 - The Further Adventures of G.I. Joe - S1-E1
Other mistake: Mutt reads the card about the "fatal fluffies." He says "I'm sure you'll enjoy their deadly secrets", but the card reads "I'm sure you'll enjoy their amazing "split" personalities."
Other mistake: In the episode where Tino is freaking out about the "FunVille" Arcade door looking like the mouth and face of a clown, it does. But in another episode I saw this morning (where Carver pretends to be all tough) the FunVille door is like any other normal door.
Misty's Magical Mix-Up!/Bone's Lucky Doubloon - S2-E31
Other mistake: In the episode "Bone's Lucky Doubloon," Captain Hook, Smee and another pirate are washed downstream, go over a waterfall and land in a lake. When they emerge from the lake, no water is dripping from them.
Other mistake: When Scooby is eating the hot dogs at the "Hotus Dogus" stand, his tail goes transparent.
Beavis and Butt-head vs. the Vending Machine - S4-E28
Other mistake: When Butt-head is purchasing the pork rinds from the vending machine, he notes that the selection for them is F2. When he is pressing the buttons to dispense them, he presses the F button twice, but never the 2 button. Somehow, the machine still dispenses the correct item.