Sonic and Tails head into a network of abandoned mine shafts to escape from Scratch and Grounder, but they are held captive there by a miserly mole named Spelunk.
This episode provides examples of:
- Adaptation Induced Plothole: The events of this episode take place in Marble Zone from Sonic 1. However, Marble Zone is depicted as a mine here, rather than marble ruins, making its name seem completely nonsensical.
- All Cloth Unravels: Sonic pulls a loose thread on Spelunk's clothes made of Diamondius threads to create a rope to stop the swinging spike balls in one of the caves, causing the suit to come unraveled and leave Spelunk in his full-body underwear. After Tails and Spelunk get through the cave, Sonic sews Spelunk's clothes back together.
- Alliterative Title: Subterranean Sonic.
- And Knowing Is Half the Battle: In the "Sonic Says" segment, Tails won't share his hot dogs with Spelunk and Spelunk won't share his chili with Tails. Sonic explains the benefits of sharing and they make Chili Dogs.Sonic: Hey! If we share, why we can turn those ordinary hot dogs into three mouth-watering, tastebud-tantilizing chili dogs! (Sonic turns to the kids) See, guys? If you share, everyone's happy!
- Attack! Attack... Retreat! Retreat!: This exchange when Grounder attempts to save Robotnik from falling down a bottomless pit:Scratch: Catch him, catch him!
(Grounder produces a net and catches Robotnik in it.)
Grounder: I caught him! I caught him!
(Robotnik rips through the net and continues falling down the pit.)
Grounder: Oooh, I didn't catch him.
Robotnik: Fools! - Burning Rubber: Sonic often leaves a trail of fire when running. He leaves a trail of fire burning behind him as he and Tails enter a diamond mine.
- Censorship by Spelling: Sonic disguises himself as an accountant to trick Scratch and Grounder, which leads to this exchange:Sonic: I see you haven't filed or declared, you haven't deducted your Y-O-Us, your A-R-Es, or your S-O-Stroke-S-T-U-P-I-Ds.
Grounder: Oh, is that bad? - Heel–Face Turn: Spelunk goes from being a miserly, selfish mole who was very protective of his treasure to someone who wants to travel the world and help people the way Sonic and Tails helped him, and being more than willing to use his treasure to pay for any expenses he might need.
- Losing Your Head: Grounder's head detaches from his body when he and Scratch follow Sonic and Tails down the geyser hole.
- Manly Tears: Spelunk cries these after Sonic saves him from being crushed.
- Meaningful Name: Spelunk's name means to explore natural caves, which is what geologists do to study natural formations of the Earth.
- Minecart Madness: When Sonic and Tails attempt to escape from the cave by running up the mountain, Spelunk rides a mine cart down it to chase them away.
- Mole Miner: Spelunk is one of these.
- Talking with Signs: Scratch holds up a sign that says, HELP! when he and Grounder see a cannonball heading for them.
- Trap Door: The cage that Spelunk traps Sonic and Tails in has one that leads to a bottomless pit.
- Water-Geyser Volley: This episode ends with Robotnik, Scratch, and Grounder being launched into the air by the geysers.
- Wingding Eyes: Grounder's eyes turn into dollar signs when Spelunk's gold and jewels rain down from the sky after he, Robotnik, and Scratch use dynamite to blast open a crater they dug.
