- This article contains spoilers.
Spooky Shell Science is based on Companion Shell, and by extension, the Portal series in general. To beat the level, the player must have Mario work through 19 unique Test Chambers of a decaying facility by solving shell-based puzzles and obstacles. Shortcuts are available in the form of side areas that take above-par skill and thinking to access.
When almost all of the Test Chambers are completed, Mario falls into a maintenance area, and discovers a Warp Pipe leading to a series of closed-off sections of the facility. He uses abandoned testing components to his advantage, navigating around and between the Test Chambers until he reaches the main control room, inhabited by ELaNOR. A boss battle ensues; Mario activates POW Blocks to disable ELaNOR's foolproofing mechanism, destroy her from the inside, and remove her power source before finally leaving the facility.
As follows is a brief description of each Test Chamber.
Koopas are introduced. The player must stomp one and kick its shell into a nearby Brick Block to continue via an elevator.
The player must carry shells to progress, rather than merely kicking them aside. There are two Brick Blocks to break, so the player is expected to realize that items respawn from pipes.
Conveyor belts, spike traps, and vines are introduced here. A Super Mushroom must be found and used to continue to the next Test Chamber. Carrying a shell into the lower part of the area, using Super Mario's mercy invincibility to jump off of the spike traps, and then collecting another Super Mushroom in midair allows access to Abandoned Test Chamber 4.
The player must bounce off of enemies to complete this Test Chamber. Note Blocks are introduced. The second challenge is much easier if the player sets down the shell and waits for the Koopa to reemerge from it.
This Test Chamber deals with Note Blocks. It also introduces Parabuzzies; Mario lands on one upon entering the area. The player has to set a POW Block onto a Note Block to progress, then jump across vines and continue into Test Chamber 6 via falling. The player breaks into this area again during the escape sequence. Donut Blocks are introduced in a previously-blocked-off area.
POW passwords are introduced. The correct solution, 4, is given on a sign. After solving the password, the player is expected to realize how the contraption works; no solutions are given after this Test Chamber. Doors are introduced, used if an incorrect password has been inputted.
The player rides and jumps off of Parabuzzies to move around the area. A three-digit POW password must be solved.
The first checkpoint is found here. Parabuzzies are used to reach an upper area, where a shell must be thrown at a Brick Block mid-jump to open a Warp Pipe.
After throwing a shell with the right timing, the player must cross a series of vines. The player reunites with their shell and breaks a couple of Brick Blocks with it to open access to the elevator.
Mario falls down a large pit into an area with conveyor belts. The player must climb a structure to make Parabuzzies start spawning, then use them to climb out of the area. The following challenge is another vine-climbing section. Finally, in the elevator, Mario has to be trapped between the lift and a Hard Block to clip him to the floor of the shaft. The player breaks into this area again during the escape sequence.
Mario falls down once more, and the player uses a Koopa, trampoline, and POW Block to climb out of the area. Additionally, the player should look at the layout of the next room to avoid impaling Mario on spike traps after a second fall. Mario then rides the elevator into the next Test Chamber.
Test Chamber 12 contains the game's second checkpoint. The player must bounce on tracked Koopas to reach another Warp Pipe. Doors are available to reset the area if needed.
The player kicks a Big Koopa's shell into two rows of Brick Blocks, quickly destroying them in the process. Mario can then advance to the next area.
Mario automatically kicks a big shell into a contraption that releases it to the right after a while. The player has to bounce off of the shell to progress, as a Bumper in the way leaves Mario unable to jump normally.
Most of this Test Chamber is in ruins. The player needs to make a tricky jump off of a Parabuzzy to continue.
This area contains the most involved puzzle yet, with a two-digit POW password, Brick Block breaking, and trampolines and Parabuzzies emerging from pipes. However, the floor has been busted open, giving the player Warp Pipe access to an out-of-bounds area.
Test Chamber 19 is largely in shambles when Mario comes across it.
This shortcut area can be accessed from a secret passage in Test Chamber 3, and completing it unlocks access to Test Chamber 10. Abandoned Test Chamber 4 is strangely detached from the preceding Test Chamber, and its monitor is smashed in, likely due to the fact that it has been abandoned. It introduces the mechanic of bouncing on enemies to gain additional height. The player must then set a POW Block onto a Note Block to continue into Test Chamber 9's elevator.
Mario enters the control room at last to fight ELaNOR. The battle begins after the player drops some Donut Blocks. ELaNOR fires Spiny shells across the floor; unlike in all prior areas of the game, shells are strictly to be avoided. The player can dodge the Spiny shells by jumping, standing on a Donut Block, or grabbing a vine. However, Mario must eventually run along the ground into a side area to hit POW Blocks. Each shockwave weakens ELaNOR's Muncher-based foolproofing, but also prompts her to fire more shells at once, making her attacks progressively harder to avoid. After three POW Blocks have been used, the player has to run directly underneath ELaNor to cause her to Thwomp the Brick Blocks on her underside. After the Thwomps rise back up, the player can collect the goal to power ELaNOR down completely. Mario then exits the facility at last.