Mushroom Kingdom Underground is the alternate version of the Batcave for Smash Bros: Stars Among Us. The Underground is the secret headquarters of Yoshi (or in the Regime Insurgency world Boshi), located under Luigi's Mansion.

Stars Among Us StoryEdit

The Underground was abandoned along with Luigi's Mansion after it became to dangerous for Boshi to stay there given that Mario knew its location, but not before hiding an atimatter Laser that can incapacitate Mario within the lead polymer lined walls along with the "vault" that only opens up the bit of the rockface containing the Laser when the DNA of Boshi, Waddle De, Link, Game and Watch, and Pit are sampled simultaneously.

Boshi was forced to transport versions of the other four from another universe due to his Pit being dead and the others supporting the One World government. Once they unlocked the case containing the Laser, they fought Regime Link and Demise, however during the fight, the laser was damaged beyond repair, although the antimatter was intact, they left to rethink their plan.

Later on, during Regime Mario's attack on both New Pork and F-Zero, the two Yoshi's moved the dimensional transporter and (after a fight between them) they brought the main Mario over to stop his evil counterpart, after quickly bringing him up to speed and making a plan for limiting any collateral damage (e.g. from a fight against Bowser) Boshi tells Mario that "it's good to have you back" before they leave. 


Crime LabEdit

  • On the left side of the stage, there are a pair of Bob-ombs that the player can use against the opponent after they come out of the ?-Block in the background
  • In the center of the stage, a player can knock the opponent against the Computer and open up for additional combos
  • On the right side of the stage, a Switch can be activated to fire the missiles of the Yoshi Car to damage the opponent. 


  • On the left side of the Lagoon, the Warp Pipe can be used to damage the opponent only with Gadget Characters. Also, a Thwomp can be found near the Mecha Bowser and can be exploded/thrown at the opponent. 
  • On the right side of the stage, you can knock the opponent into Brick Blocks to reveal a Egg Block with a Yoshi Eggs that come out of it. The Egg can be thrown at the opponent, and the Block will reload with another available Egg after a brief moment. 

Stage TransitionsEdit

  • On the right side of the Crime Lab, a transition can be performed that will send the opponent falling through the debris of the Underground, leading them below to the Lagoon.
  • On the left side of the Lagoon, a transition can be performed that will send the opponent plummeting into the Warp Pipe where they are beaten repeatedly until they are ejected out into the Crime Lab.

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