Start off by clearing out the Boomerang Bros on the first two platforms, being mindful of the Lava Bubbles. Look to the back left to see Green Star #1 hovering just above the lava in the crack. To reach it, hop up past the spinning Fire Bars, then wallride the left wall, wall jumping at the last moment to grab the star. If you took the advice earlier, use your Cat Suit to easily grab the Green Star and hop back up, although it is not needed here.
Ahead is a Kick Bomb cannon, along with some Flopters and some grey bricks on the back wall. Kick a bomb into the grey bricks, revealing a P-Switch, but don’t hit it just yet. Instead, wall jump in this little alcove up to the top and collect the Stamp. This is where you will need the Cat Suit now, so make sure you don’t accidentally touch the P-Switch after collecting the Stamp. See that tall wall blocking your way on the right? Climb up to the top of it and collect Green Star #2 here. It’s very difficult to get this star without using this method.
Go ahead and finally hit that P-Switch now, lowering the bridge and allowing you to continue. Across the bridge will be a Fire Bro, as well as a Ka-thunk. Past them will be some Kick Bomb cannons, but avoid touching these, as they will hurt you (flashing red). The Checkpoint Flag will be right past the pairing of Fire Bro and Ka-thunk. Switch to the Boomerang Power-Up as you move to the next area.Run across the small bridge with all of the Lava Bubbles, then boomerang Green Star #3 over the lava. Cross another thin bridge, then jump at the small metal plate on the ground to reveal a hidden block that contains a Boomerang Flower.
The last obstacle before the end here will pit you against two Ka-thunks and two Hammer Bros. If you have the Boomerang Flower active, then you can simply wait for the enemies to jump in the front and hit them there. Defeat both Hammer Bros to clear the way to the Warp Box, where Bowser will be waiting once more.
Boss: Bowser’s Highway Showdown Part Two
Bowser returns in his decorative vehicle, spitting lava pools and chucking Kick Bombs, just like before. The course is definitely rougher than back in World 1, as you have to contend with pitfalls, lava geysers, rows of spikes, and narrower paths. Be patient as you avoid all the obstacles, until you can kick a Kick Bomb back at the King of the Koopas. If you run out of track there is a Warp Box that takes you to a grated floor where lava geysers become more frequent and the pathway is definitely more narrow. Keep calm and land enough Kick Bombs back at Bowser to take him out.
Once you defeat him, you can take the Warp Box to the Goal Pole area and finish off this world.