Start off by clearing out the Boomerang Bros. on the first two platforms. 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 flames 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.
Ahead is a Kick Bomb cannon, use it to kick some bombs into the wall revealing a P Switch . Ignore it for now and use your Cat Suit to climb up the wall near the grated bridge you haven’t dropped down yet. At the very top is Green Star #2 and the Cat Suit is the only way to obtain it. Hop back down near the P Switch, but instead wall jump or climb up the corridor to the Stamp .
Finally, hit the P Switch to lower the bridge where a Ka-Thunk, Fire Bro, and Bomb Cannons await. Defeat the Fire Bro then time your run past the cannons to reach the Checkpoint . Switch to the Boomerang Power-Up as you move to the next area. Boomerang Green Star #3 over the lava then race to the end where a ? Block hovers over a symbol. Ground Pound it for another Boomerang Flower then defeat the Hammer Bros. so you can jump through the Ka-Thunks and reach the Warp Box.
Boss: Bowser’s Highway Showdown Part Two
Bowser returns on his decorative vehicle, spitting lava pools and chucking Kick Bombs. The course is definitely rougher than back in World 1, 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.
Like usual, grab the Green +Clock on the way to capping the Goal Pole.