The Lava Queen was apparently summoned by the MegaBug to stop the heroes's advance, as it is shown dropping a red orb (similar to the ones that summoned Bwario and Bwaluigi) further into the Pits as it flies away with Spawny. She appears in person when Bwario and Bwaluigi appear for a rematch, sneaking up behind Mario and giving him a surprise hug and kiss. After being defeated, she blows Mario a kiss before running off with the other villains.
The Lava Queen behaves much like a Valkyrie in battle, with a similar gatling attack (that can inflict Vampire on its targets) and the ability to create shockwaves if she performs a Team Jump. However, instead of protecting her allies with shields, she can scream to force the player characters away from her. In addition to Bwario and Bwaluigi, she is supported by Lava versions of a Ziggy, a Hopper, a Buckler, and a Supporter - all seven enemies must be defeated to claim victory.