Clear Sunken Ghost Ship to raise the valley entrance. The regular route reaches Larry and the Front Door, while the secret route through Valley Fortress opens the Back Door. Both entrances finish with the same Bowser battle.
Sunken Ghost Ship
Swim into the wreck past the cannons. In the ghost section, stop in an open space when the swarm appears and move through the gap after it vanishes; do not keep swimming blindly into new ghosts. The final pipe begins a long fall with stars and Dragon Coins. A cape slows your descent and gives time to steer between them. Near the bottom, aim right toward the platform holding the green goal orb instead of dropping beneath the screen. Touching it raises the entrance to the Valley of Bowser.
Valley of Bowser 1
Use the branching cave corridors to work around the Mega Moles. Where a Chuck blocks the next passage with yellow or blue blocks, let its attack break the barrier before moving through. After the checkpoint, the upper route crosses the Muncher gap and reaches the high 3-Up Moon passage. Follow the lower branching routes onward to the final Dragon Coin, then enter the low green pipe to reach the goal. There is no secret exit in this stage.
Valley of Bowser 2
In the rising-sand maze, wait inside each recess until the next passage is wide enough; a Mushroom does not protect you from being crushed. Beyond the maze pipe, the first rising mass in the third section reaches ceiling height. Stand on its left edge, ride it up and jump onto the ceiling to the left. Walk all the way left to the key and keyhole for Valley Fortress. On another run, continue right past the Mega Moles above the Munchers to the ordinary goal and Valley Ghost House.
Valley Fortress
Advance between the Skewers only after they have risen, checking the spikes on the adjacent walls before jumping. The later Skewers move faster, and the lava gaps leave little room to recover. Use the solid ledges as waiting points rather than trying to pass two crushers at once. At the end, defeat four Reznors. This opens Bowser’s Back Door, a shortcut that starts in the castle’s final dark corridor.
Valley Ghost House
Cross the first room to the main hallway. Use the P Switch over the entrance to reveal the timed doors. The ordinary exit route leads to Valley of Bowser 3. For Larry’s Castle, activate that switch and run to the farthest-right door before it vanishes. In the next room, carry the second P Switch to the right, reveal the Control Coin and steer its trail up toward the upper-right recess. Press the switch to turn the trail into steps, then climb into the narrow passage to the keyhole. Small Mario fits directly; a larger Mario must duck or slide into the opening.
Valley of Bowser 3
The numbers on the Count-Lifts show how long they remain after you land: platforms marked 1 fall much sooner than those marked 4. Choose the next landing before stepping onto a short-lived lift. Use the springboard for the checkpoint. Beyond it, Banzai Bills cross the platform route, so land on a stable surface or bounce from a safe enemy rather than waiting on an expiring lift. Take the ordinary goal to Valley of Bowser 4.
Valley of Bowser 4
Watch the rocks thrown by Diggin’ Chucks as you cross the cave. The early green pipe visits an icy Dragon Coin room and returns to the earlier blue pipe. Climb the nearby vine to hatch Yoshi, then keep him through the checkpoint and the later Chuck sections. Just before the goal, use his tongue through the wall to take the enclosed key and bring it to the keyhole above. This opens Star Road and the Front Door. Return for the normal goal, which opens Larry’s Castle.
Larry’s Castle
Follow the snake platform around the Ball ’n’ Chains and spikes. Staying on it beyond the first high door reaches the checkpoint and the lower collectible section before rejoining the same next room. Let Magikoopa’s shots remove the blocks obstructing the later corridor, or use a cape where appropriate. Larry fights on Iggy’s tilting platform, now with extra Lava Bubbles. Stomp him when the slope will send him toward an edge, then avoid the fireballs while waiting for the next tilt. Knock him into the lava to open the Front Door.
Front Door and Back Door
The Front Door is reached from Larry’s Castle or the connected Star Road. Choose one room from doors 1–4, then one room from doors 5–8; you do not need to clear all eight. All choices join the dark corridor with Mechakoopas and Ninjis. Hit the red ? Block for the spotlight and continue to the boss door. Clearing Valley Fortress opens the Back Door, which starts in this dark corridor and includes a checkpoint. It does not contain four additional challenge rooms.
Bowser
Stomp a Mechakoopa, pick it up and throw it upward so it falls onto Bowser’s exposed head. Hitting the Clown Car itself does not damage him. After two hits, avoid the falling flames and collect Peach’s Mushroom if needed. In the second phase, Bowser drops two large steel balls before supplying more Mechakoopas. Clear the balls, then return two more Mechakoopas. After another fire shower, the Clown Car bounces toward you: move out of each landing and use the next Mechakoopas for the last two hits.
The SNES ending finishes on the final screen. Save your other exits at an available save point before entering Bowser’s Castle; defeating Bowser does not provide the GBA version’s post-ending save flow.