- For the track of the same name, see Thundersnail (Soundtrack).
The goal is to encourage the yellow snail in the top lane to win the race. Encouraging her as she crawls across the track makes her go faster. Too much encouragement, however, causes the snail to flip over and light on fire; encouraging her too little makes her believe her best was not enough.
If the yellow snail manages to win the race, the protagonist only receives 9G back as Napstablook needs to make a profit. If the snail loses by a slim margin, Napstablook observes that the snail thinks she won, and rewards 30G so as to not hurt her feelings.
To win 30G consistently, press [Z] 7 times at the start of the race. When your snail nears the finish line, press [Z] every time the exclamation mark disappears to effectively stall your snail in place.
- The minigame is likely a reference to the SpongeBob SquarePants episode, The Great Snail Race. In the episode, SpongeBob enters his snail Gary into a race, but because of being overworked before the contest, and being pushed too far during the event by SpongeBob's abusive "encouragement," Gary veers far off course and literally bursts into flames.
- The name of the game, "Thundersnail" may be a parody of the name "Undertale," seeing as they both rhyme.
- If the protagonist does not have 10G, Napstablook will still allow them to play, taking whatever money they have.
- On a Genocide Route, the protagonist is unable to play this game, as both Napstablook and the snails are absent.
|Puzzles||Waterfall • Snowdin • Ruins • Hotland • Ball Game • Multicolor Tile Puzzle • Thundersnail • Bridge Seed|