Underchomp is a boss in Super Paper Mario. It is a Chain Chomp who is based on Cerberus from Greek mythology who guarded the gates to the Underworld and had three heads. The Underchomp is found in the Underwhere, which is, apparently, the underworld of the Mario universe where Mario goes after he dies in Chapter 6 of Super Paper Mario.
He is unleashed by Doorguy the Third as a test. The battle is unique as it is like a classic turn-based RPG battle in which the Underchomp and Mario and co. each have one attack a turn. When Mario is fighting the Underchomp he can use the Pixl, or Piccolo, to put him into a deep sleep. Doing this makes the battle much easier, but the battle itself is very difficult without Piccolo. In the fight, Mario can take massive amounts of damage as well as die with ease. During the fight, Mario can use his partner's special powers as well as use Pixls and Items.
- When Mario uses Piccolo to put the beast asleep, it is in reference to a Greek myth in which the hero plays music to calm the beast to sleep and sneak past.
- The Underchomp that resides in the Underwhere, the underworld of Mario, is a reference to Cerberus from Greek mythology as it has three heads and guards the gate to the Underwhere.
- The battle system is a reference to the Japan-only Mother for the Famicom.
- The Underchomp's name comes from the term "underdog." This is funny as the Chain Chomps are considered the "dogs" of the Mario series.