Chief Chilly

Chief Chilly is the boss of the Chief Chilly Challenge, and unlocks Wario when defeated. They are a larger version of the Chill Bully with a mustache.

Battle
The battle is in an arena of an ice platform. They function the same as a Bully, attempting to charge towards the player and knock them off of the platform. They also need to be knocked off the platform. When knocked off the platform once, they will knock parts of the platform off and go back to functioning as a Bully. This must be done 3 times to defeat Chief Chilly and unlock Wario.

Chilly Chungus
An entity known as Chilly Chungus can sometimes appear and replace Chief Chilly, though they simply function as a reskin.

Yoshi Battle
Found in the files of Super Mario 64 DS is text that implies Chief Chilly would have been fought with Yoshi. However. it is only possible to fight Chief Chilly as Luigi.