- SpongeBob SquarePants
- Patrick Star
- Squidward Tentacles
- Eugene H. Krabs
- Sheldon J. Plankton
- Incidental 42
- Incidental 49
- Con man
- Judge (female)
- Karen Plankton (voice only)
- Incidental 40
- Jack M. Crazyfish (cameo)
- Sea monster (debut)
- Incidental 119
While jellyfishing in Jellyfish Fields, SpongeBob and Patrick encounter an object sticking out of the ground in the beginning of the episode. They decide to dig it up, and they discover an old submarine. Meanwhile, at the Krusty Krab, Squidward and Mr. Krabs think of an idea to bring the Krusty Krab to the customers. SpongeBob and Patrick drive the submarine into the Krusty Krab, which gives the idea to Mr. Krabs to have SpongeBob and Patrick take the submarine and sell Krabby Patties to any passersby. Seeing this, Plankton gets upset since he had the idea years ago. He takes the fist of the Chum Bucket and uses it as a mobile Chum Bucket.
SpongeBob and Patrick are unsuccessful with their first customers, so SpongeBob offers to pay them to take the Krabby Patties, which they agree to. Meanwhile, Plankton attempts to sell food to a child, whom he then insults out of impatience. All of a sudden, the child's parents, great grandmother, and various other fish start throwing rocks at Plankton. Soon, the mob runs out of rocks, but since Patrick was not paying attention to the Krabby Patties, they burned and hardened. SpongeBob and Patrick are able to sell the burnt patties to the mob for them to throw, and the two friends head off.
Later on, SpongeBob and Patrick fall into an abyss and wake up a ginormous sea monster who has been asleep for the past 79 years. Starved after his hibernation, the monster purchases 640 Krabby Patties. However, just as SpongeBob and Patrick are running out of patties, Plankton's Chum Bucket vehicle comes crashing into the submarine. Chum squeezes through the cracks of the submarine, so SpongeBob and Patrick decide to use the chum to make the burgers, which the monster ends up enjoying even more than the Krabby Patties. Plankton sees the sea monster hand SpongeBob and Patrick giant dollar bills in exchange for the chum burgers, and he attempts to get the monster to refuse the food. However, Plankton is mistaken for a chocolate éclair and the monster chases him away. Meanwhile, because they are down in the abyss, SpongeBob and Patrick have to let go of all the money they have earned to float back up to the surface. Instead of money, they bring back 37,000 pounds of decorative undersea rocks, much to Mr. Krabs' disappointment.
- SpongeBob drives the submarine and bumps into the Krusty Krab, destroying the front window.
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
‣ Once Upon a Time - Gregor F. Narholz [title card]
‣ Towerstreet 17 [#6] - Gerhard Narholz [SpongeBob and Patrick with walkie-talkies]
• Sponge Monger - Sage Guyton, Jeremy Wakefield [running away from the jellyfish]
• Nude Sting - Nicolas Carr [Patrick lands on a rock]
• Goofy Conversation - Nicolas Carr, Barry Anthony [Squidward sunbathing/Large piles of dirt behind SpongeBob and Patrick]
‣ Cosmos Adventure - John Fox [submarine unearthed]
‣ Weird Bridge - Roger Roger [SpongeBob and Patrick get inside]
‣ Missile Disaster - John Fox [submarine takes off]
• Grass Skirt Chase - Sage Guyton, Jeremy Wakefield [SpongeBob and Patrick fight over the steering wheel]
‣ Keel Row - Brian Peters [Krusty Krab empty]
• Steel Licks 20 - Jeremy Wakefield [submarine crashes]
• Harp! - Nicolas Carr ["That's it!"]
• Skipping to School - Sage Guyton, Jeremy Wakefield ["So long, lad!"]
‣ Zelle 501 - Gerhard Trede ["A traveling restaurant, eh?"]
‣ Towerstreet 17 [#25] - Gerhard Narholz [fist submarine takes off]
‣ Tripping Upstairs - Brian Peters [SpongeBob and Patrick selling Krabby Patties]
‣ Hercule Poirot - Gerhard Trede ["Thank you, sir, come again!"]
‣ Off to Play - David Snell [Plankton approaches a little kid]
• Tension Bits - Nicolas Carr, Sage Guyton, Jeremy Wakefield [Plankton insults a family]
• Steel Licks 3 - Jeremy Wakefield ["You're probably right."]
‣ Dramatic Cue (C) - Ronald Hanmer [everyone throws rocks at Plankton]
‣ The Rake Hornpipe - Robert Alexander White [Patrick burned all the Krabby Patties]
‣ Dramatic Cue (C) - Ronald Hanmer [Mable's husband throws the last rock]
• What's This - Nicolas Carr ["Hey, the rocks are all gone!"]
‣ Dingles Regatta - Brian Peters [everyone buys the burnt patties]
‣ Dramatic Cue (E) - Ronald Hanmer ["Oh, okay. What's an abyss, SpongeBob?"]
‣ Dramatic Cue (B) - Ronald Hanmer [Submarine fails into abyss]
‣ Dramatic Cue (G) - Ronald Hanmer [Plankton cheers as the submarine continues to plummet]
‣ Monster Bug (a) - Gregor F. Narholz [sea monster wakes up]
‣ The Rake Hornpipe - Robert Alexander White ["Look, Patrick, we floated back up!"]
‣ Monster Bug (a) - Gregor F. Narholz ["Who are you calling dark and depressing?!"]
• Vibe Q Sting - Nicolas Carr ["Hungry?"]
‣ Kerry Polka - Brian Peters [sea monster enjoys Krabby Patties]
‣ Like Strange - Kenny Graham [Plankton spying on them]
‣ Flare-Up - Robert Pagan [chum charges]
• Steel Licks 6 - Jeremy Wakefield ["I sunk the Krusty Krab!..."]
‣ Dramatic Cue (D) - Ronald Hanmer [Plankton's submarine crashes]
‣ Glissando (H) - Skaila Kanga, Richard Myhill ["Who needs that rust bucket anyhow?"]
‣ King of the Giants (a) - John Fox, Otto Sieben [sea monster demands more food]
• New Vibe Hits 2007 - Nicolas Carr [Sea monster sees the Chum Patty]
• Birth of the Krabby Patty - Nicolas Carr ["Mmm... now that's a sandwich!"]
• Happy Sponge Chase Vibes - Nicolas Carr [more chumwiches]
‣ King of the Giants (a) - John Fox, Otto Sieben [sea monster demands dessert]
‣ Editor's Falling Over (F) - Dick Stephen Walter [Plankton falls and gets covered in dirt]
‣ Cartoon Capers (C) - Dick Stephen Walter [Plankton rolls down the abyss]
• Earl's Revenge - Sage Guyton, Jeremy Wakefield [sea monster chases Plankton]
‣ The Tip Top Polka/The Cliff Polka - Chelmsford Folk Band [back at the Krusty Krab]
‣ Captain Lenoe's - The Folk Players [ending]
- "Jellyfishing" (1999) - Footage of a jellyfish swimming around at the beginning is actually reused from this episode.
- "Krabs à la Mode" - The animation of Plankton's telescope shaking was reused.
- This episode is available on the SpongeBob's Pest of the West, SpongeBob's Atlantis SquarePantis (UK version), Season 5 Volume 2, SpongeBob StarPants, First 100 Episodes, The Super Celebrations, Really Big Box Set, The Ultimate SpongeBob Box Set, SpongeBob SquarePants Vol. 8, The SpongeBob Super Square Collection, Complete Fifth Season, Beware the Hooks, From the Beginning, Pt.2, The SpongeBob SquarePants Collection, On the Road, The Inmates of Summer, The SpongeBob SquarePants 8 Season DVD Collection, and The Best 200 Episodes Ever DVDs.
- "20,000 Patties Under the Sea" was ranked #8 during the SpongeBob's Top 100 event in the UK and Ireland from June 4-8, 2012.
- This is so far the only episode where the title starts with a number.
- The first couple seconds of animation are reused from "Jellyfishing," making it the fourth episode to use footage from a past episode. The first is "Ugh," the second is "The Sponge Who Could Fly," and the third is "Mrs. Puff, You're Fired."
- The con man from "Chocolate with Nuts" returns in this episode and cons SpongeBob and Patrick one more time, this time without even trying, as they hand him money for trying some Krabby Patties. It seems like he remembers SpongeBob and Patrick since he says, "Hey, thanks again, guys."
- Plankton's line "Someone should put you in a box, floating down the river, grandma!," has become a popular meme on YouTube, due to how insane the roast is.
- Jack M. Crazyfish, who first appeared in "Blackened Sponge," can be seen hurling things at Plankton. His voice sounds different in this episode than in his debut.
- The sea monster is voiced by Gene Simmons, who is well known for being the bass player for the band KISS.
- The mother who is insulted by Plankton is voiced by Simmons' partner, Shannon Tweed.
- In a way, SpongeBob and Patrick helped the Chum Bucket more than the Krusty Krab because the sea monster preferred Plankton's chum over the Krabby Patties.
- During the Craziest Creatures marathon it was paired up with "Giant Squidward."
- SpongeBob confirms that the Krusty Krab does not have desserts on the menu.
- The closest thing is a triple Krabby Patty with five scoops of ice cream, which later appears in "Drive Happy."
- When the monster mistakes Plankton for dessert, he breaks the fourth wall by looking at the screen and saying, "Now that looks like dessert to me!."
- If counting this episode segment and its sister as one episode instead of separate segments, the previous and next episodes are both specials in between this episode.
- In the Welsh dub, this episode is called "Crancdy'n Crwydro," which translates to "Spraying Crab."
- In the Indonesian dub, the scene where Plankton gets thrown/SpongeBob and Patrick selling burnt Krabby Patties was skipped to SpongeBob and Patrick finding an abyss. This was done either due to time constraints or throwing rocks scene was deemed too violent.
- The title is a spoof of Jules Verne's classic novel 20,000 Leagues Under The Sea, which revolves around its characters traveling the ocean in a submarine and encountering strange creatures.
- This novel is also referenced in "Scavenger Pants."
- At one point, the lens of SpongeBob's jellyfishing glasses are the wrong shape.
- There is a short distance between the grass in Jellyfish Fields to the submarine stuck in the ground, but later, the grass does not appear.
- In addition, it is shown in numerous episodes there is not any grass around SpongeBob's and Patrick's houses.
- As SpongeBob and Patrick are running away from the jellyfish, SpongeBob's left shirt sleeve is not colored in for a split second.
- Usually, the series is shown that any underwater creature is much smaller than anything on the surface, but in this episode, it is shown that the submarine and the human skeleton are the same sizes as SpongeBob and Patrick.
- In the Krusty Krab, in one shot, the cashier boat is floating, but it is on the ground in the next shot.
- When the sea monster takes the submarine off his head, the periscope at the top of the submarine is missing.
- When Plankton says, "Ah, who needs that old rust bucket anyhow?", his voice is out of sync with the animation.