Start by moving up to the Green Star Ring and collecting the eight Green Coins to spawn Green Star #1.
Collect a Super Bell to gain the Cat Power-Up, then climb atop the back wall for a Green +Clock before continuing right. Ride the moving platforms over the gap then kick one of the Kick Bombs into the wall to the right revealing the Stamp .
Now climb up the wall above the Stamp and hit the Cat Wheel to raise the platform. Climb to the top and jump across to the right to find Green Star #2 . If you drop down from here you can land atop some Thwomps to find more Green +Clocks . Continue up the pathway and defeat the tower of Goombas to get Green Star #3 then continue to the final area before the boss fight. Use the Kick Bombs to blast away the back wall and reach the Warp Box.
Highway Showdown with Bowser
Bowser rides in his vehicle tossing Kick Bombs at you but you can kick them back to deal damage. Direct hits to Bowser deal more damage than hitting the vehicle but either way is effective. You need to watch out for the Kick Balls that are about to explode and the lava pools that Bowser will spew onto the path. If you move through this battle long enough the scenery will change a bit and Goombas join the fray. Land several hits on Bowser or the vehicle to end the battle then use the Warp Box to reach the final area.
Claim the Green +Clock and jump atop the Goal Pole to save the Sprixie Princess. She will create a pipe to access World 2 if you haven’t already done so in World 1-2. Head on over to the next World!