As soon as you begin to traverse the level, several green magic projectiles begin to come across the screen from the right.
Boss Battle
This time, Iggy has gotten into a carriage that is being pulled along a rectangular rail by a massive Chain Chomp! Wait for the Chain Chomp to pull Iggy along the rail and then drop down on his head from above.
After you hit him, the Chain Chomp will get extremely upset and yank Iggy around the rail while it tries to bite you. Stay ahead of the massive chomper and either use the bouncy blocks at the edges of the room to hop back up to the ledge above the ground, or Wall-Jump back onto it. Continue to stay ahead of the Chain Chomp and hit Iggy three times on his head to defeat him.