Immediately prior to the boss battle, the Icicle Golem freezes Mario and his allies in blocks of ice. Princess Peach arrives and frees two of the heroes (Mario and whichever Rabbid hero is in the second team slot), but the Icicle Golem throws the third character into its fridge before they can be defrosted; thus, Peach herself rounds out the party for the boss battle.
Initially, the Icicle Golem uses a refrigerator door as a shield - much like a Buckler, this renders him immune to frontal assault. He fires blasts of ice from his cannon-like right arm; like a Blastgun, this hits a cone-shaped area around his main target, hitting everyone in range for 30 HP and a high chance of being Frozen. The heroes must work together to flank the boss and hit him from his vulnerable sides and back, slowly depleting his HP.
In the second phase, the Icicle Golem loses his shield, but gains a close-range fist pound attack that deducts 70 HP from the targeted character and 35 HP from everyone within a square or two of the impact point. It also begins using a "line of sight" technique that allows it to attack heroes moving within its vision range on their turn. At the end of the boss's first turn in this phase, a pair of Sherbet Smashers spawn on either side of the arena. Mario and his allies must manage the new enemies along with the main boss as they wear down its HP a second time.
In the third phase, the Icicle Golem's legs melt off as it crawls to the far end of the arena, where it remains for the rest of the battle. It continues using its old attacks, but its "line of sight" counterattack can be activated much more frequently. It also gains a pair of Sherbet Supporters at the end of its first turn; the Rabbids appear on either side of the Golem, and should be dealt with quickly to prevent them from disrupting the party and healing the boss.
Once its HP is depleted for the third time, the Icicle Golem's body will collapse, leaving its head on the ground. The head no longer attacks or moves; all the heroes have to do is hit it with a dash attack to knock off its lower jaw and end the battle. In the post-battle cutscene, the Rabbid member of the party(usually Rabbid Peach) picks up the boss's head, plays with it for a moment in a manner similar to a scene from Willaim Shakespeare's Hamlet), then sets it down for Peach to kick back into the giant refrigerator from whence it came, freeing the trapped member of the party in the process.