Part 4

After the tutorial battle, go left into the next room.

Go right to find a ? block containing three 1-Up Mushrooms. Continue right into the next room.

Go to the right and onto the gray platforms to find another ? block containing three Mushrooms.

Jump towards the right side of the room, avoiding the yellow substance (by pressing A and B simultaneously), then head right to the next room.

Go right to the elevator. Press the corresponding character's button on the block above them when it lights up to make the elevator ascend. The pattern will alternate. After landing, go right into the next room.

Head right to find a crate with a hammer emblem and two more unmarked crates. Use the nearby Emoglobin (if I recall correctly) to save, then go right into the next room. You cannot yet obtain the hammers.

In this room, jump over the gap and get under the multicolored box to receive one of ten Trash Pieces. Collecting ten Trash Pieces teaches you a Special Move, a more powerful move that costs SP.

Go right, over the gap, and hit the ? block to find three Syrup Jars, which restore used-up SP. Go right into the next room.

In this room, check all corners to find eight more Trash Pieces. After finding all but #10, go through the newly-opened exit in the top-left corner.

Hit the multicolored block to receive the final Trash Piece. You will receive the Special move Green Shell. Enter the tutorial when prompted to learn its use.

After exiting the menu, use the Green Shell Special move to defeat the enemies. Leave to the left.

Arrive on the upper level of the hammer crate room. Go left and hit the ! block to fall, breaking the crate and revealing two hammers.

To use hammers in the field, switch to their icon via R. Go to the right and break the crates to leave.

Fall down and break the crates that impede you. Go to the far right and hit the red switch with the hammer. Break the falling rock.

Two Spike Blops appear; you'll receive a tutorial on battling with hammers. After this battle, go into the pipe and shoot yourself to the platform, then go right to find the next room.

Hit the ? block repeatedly to receive 25 Coins. Go along the linear path, defeating enemies and hitting another ? block for three Syrup Jars. Go through the exit to arrive in "Bowser's World Map".

Move to the circle marked with the Mushroom emblem and press A to go to Toad Square.

In Toad Square, go right and down to find the "inn" - for 10 Coins, you can drink juice to fully restore Mario and Luigi's HP and SP. Go to the center-right for an item shop, top-right for an advice counter, and top-left for an equipment shop (currently unusable). Exit when ready.

Go to the Funny Bone on Bowser's World Map.

After a short scene, go right and bash the yellow thing (the nerve of the funny bone). Bowser awakens and you regain control of him in Cavi Cape Cave.

Upon regaining control of Bowser, go east to the next area.

Press A/B to control the Bros.; press X/Y to control Bowser. Go north, using X to break rocks.

Reach a wooden bridge. Step onto the metallic panel near the edge. Punch a falling metal ball to hit the switch and unlock the way to the next area. Go to the next area.

Go west and you'll find a spider web. Bowser's fire is currently stopped. After a short scene, go north and to the next room.

Save and go onto the big, green-ish block. It will move. Beware of stony outcroppings; punch them to remove them.