Continuity mistake: After Mario drains the dungeon, Toadstool and Toad jump off the shackles they were hanging off. However, when Mario jumps off, Toad is again seen hanging from the shackles even though he had previously jumped down. The next scene confirms this by having him on the ground where he belongs. (00:10:28)
Continuity mistake: When the mother Birdo lands at her house, the chairs at the table have their backrests without cushions, but in the next shot, cushions appear on them. (00:03:45)
Continuity mistake: When the limousine drives down the street, it has the US and USSR flags on the front of the limousine, but when water pushes it back, the flags change to generic red and yellow flags. (00:12:19)
Continuity mistake: When the crocodiles approach the general store, the store's front door has its doorknob on the left, but in the next shot, it appears on the right. (00:06:26)
Continuity mistake: When the ketchup lorry crosses the bridge, it has a cream cab and a red trailer, but in the next shot, it has a blue cab and a grey trailer.
Revealing mistake: When the camera pans across the front of Double Cross Ranch, the edge of an animation cel is visible. (00:13:51)
Revealing mistake: When a front view of King Koopa running down a street is shown, he clips through a building. (00:15:25)
The Koopas are Coming! The Koopas are Coming! - S1-E35
Continuity mistake: Just before the pillory is destroyed, it is violet, but in the next shot, it is orange. (00:14:37)
Audio problem: When King Koopa throws the snake at the Mario Bros., they use Luigi's voice when King Koopa says "Quick, quick! Run away from him!"
Revealing mistake: When the camera scrolls to Grunt (in the scene where the gang are locked up in a cell, being watched a strong, non-human security guard named Grunt), he appears out of thin air. The animators might have had some trouble putting him into the scrolling shot. (00:11:15)
Character mistake: When the Koopas chase Mario and Luigi, the sign says "COOPA ISLAND" instead of "KOOPA ISLAND." (00:06:39)
Character mistake: When Koopa is chased by a cop, he passes a Burger Shop. The sign says "BURCER SHOR" instead of "BURGER SHOP." (00:04:35)
Character mistake: The title card says "Plummers Academy" instead of "Plumbers Academy."
Mario meets Koop-Zilla - S1-E28
Continuity mistake: When Mario is eating sushi, he eats it with a fork, but his fork disappears and a spoon appears out of nowhere.
Mario meets Koop-Zilla - S1-E28
Continuity mistake: After when Luigi says "It's an earth shake!" when he flips, his straw hat changes into his green cap in mid-sentence. (00:03:58)
King Mario of Cramalot - S1-E2
Audio problem: At the end, when everyone is laughing, Toad's mouth isn't moving. (00:18:43)
King Mario of Cramalot - S1-E2
Revealing mistake: When king Koopa says "I don't know. What?", his spikes disappear. (00:15:56)
King Mario of Cramalot - S1-E2
Audio problem: When Toad says "that was close", his mouth isn't moving. (00:11:29)
Rolling Down the River - S1-E5
Continuity mistake: When the Koopa Troopas discover that Mario and Luigi cheated, Mario's gloves disappear. (00:05:29)
Rolling Down the River - S1-E5
Continuity mistake: In one shot of Toad being thrown into the dungeon, his blue trousers turn white. (00:04:48)
