SpongeBot SteelPants appears a bigger, metal version of SpongeBob SquarePants in karate gear. Jet flames are present where SpongeBob's legs would be, allowing SpongeBot to fly (which would also damage SpongeBob if he got close to them). The robot's mouth contains a large speaker as well as large white metal plates that emulate SpongeBob's iconic buck teeth. Rehydrated also adds to or modifies some of SpongeBot's steel plates and bolts, along with giving the robot an extra row of bottom teeth and one screw on each side of his hips.
SpongeBot's eyes are transparent with blue irises. In the console versions of the original Battle for Bikini Bottom, the eyes' transparency appeared yellow (likely due to showing the inside of his head), the irises were circular, and the eyelashes disappear only in its Anchor Arms form. In all versions of Rehydrated, the eyes' transparency appears blue to match SpongeBot's internals, the irises are hexagonal, and the eyelashes are completely replaced with metal frames that encompass the entirety of the rims of its eyes.
When the player fights SpongeBot from the outside, nine green lights that function as power generators appear on the robot's body: one on each glove, one on each corner of its face, one on each side of its body, and one on the tip of its nose. The player must shatter all of these lights to damage it and advance the fight. If SpongeBot hits SpongeBob with any move except its horizontal chop, it's taunting animation is an eerie mimic of SpongeBob's signature laughter in its robotic voice.
The inside of SpongeBot's body contains a large metallic brain as well as many platforms being raised by jet flames. Some of these platforms have Duplicatotrons that spawn robots. Fuses that power SpongeBot are located throughout the body with three of them powering the brain. SpongeBot shuts down if the three fuses in its brain are destroyed.
Game Boy Advance
SpongeBot appears similar in the Game Boy Advance version of Battle for Bikini Bottom. Instead of karate gear, SpongeBot wears a Krusty Krab employee hat; one of its arms is replaced with a spatula and the other is replaced with a clamp. The robot also has glowing red eyes instead of transparent ones, as well as a red antenna on the back of its head. Overall, the robot is much smaller in size than the robot seen in the original console and Rehydrated versions of the game.
Karate Slash: SpongeBot performs a horizontal slash, swinging one of its arms across the tops of several platforms. After this attack, he freezes in place, allowing him to normally be safely attacked during this period before he recovers. Curiously, the robot's left arm is frozen more inward, while his right arm is frozen outward. Also, having this attack connect on SpongeBob does not make the robot trigger its taunt animation whatsoever.
Whenever the robot is damaged during this phase of the attack in the original console version via 2 segments of each HP phase remaining, it will recoil and slap itself in the face to knock itself unconscious (whereas damaging him at any other time outside of this state results in his normal pain animation before becoming unconscious). This minute detail somehow no longer occurs in the remake.
In the remake, the cue for this attack is more obvious as the robot sticks out his hand after stiffly prepping it just before chopping. Unlike the original, the robot's placement for either arm is now more even along with its orientation upon freezing in place.
Karate Chop: The 2nd phase attack addition. SpongeBot preps up as he moves forward towards SpongeBob's position, and performs one or more vertical chops depending on how much HP it has left, each one flipping a platform.
In the original versions, the flipping platforms can be used to rocket SpongeBob off into a high height via making use of the momentum if timed right. However, in the remake, the platforms themselves now damage SpongeBob while flipping as indicated by a red outline glow.
KAH-RAH-TAE Cry: The 3rd phase attack addition, just before it performs its karate chops again. SpongeBot upon rushing up to SpongeBob, shouts "KAH-RAH-TAE!", causing the words themselves to appear above the robot. "RAH-" flies towards a platform, then "KAH-" and "TAE!" fly towards the two platforms on each side of the first one. The words each cause a platform to flip upon moving past them, and it will repeat this process a few more times depending on its HP amount.
In the remake, the platform physics functions the same way as with the chop, meaning this attack can no longer be avoided by avoiding either of the outer words by jumping back towards the first-flipped platform without waiting/timing it to avoid damage.
On the Game Boy Advance version, SpongeBot makes a Krabby Patty Bomb and lobs it downward using its spatula.
Its main weak points in the first battle are the aforementioned nine green lights which act as power generators; once one is shattered, it will remain broken for the duration of the fight. Each time at any two segments of its HP phases remaining when damaged, SpongeBot will become unconscious which prompts Robo-Plankton to take over during that phase by periodically firing his beams at the player. Robo-Plankton then must be hit at least once which will cause SpongeBot to wake up to start its next phase.
If the player ends up on the bottom portion of the arena during this time when SpongeBot is inactive but if Robo-Plankton has already been attacked, SpongeBob must bounce back up to the platforms first in order to have the robot awaken.
Most of the time, unlike several other bosses where they normally can only be damaged during certain periods of their fights, it is possible to damage SpongeBot's weak points with basically any attack possible that can reach, and at any time throughout the fight, though doing so is a rather risky outside of it freezing in place from its sideways chop. Most of the time, however, the Cruise Bubble move is required to shatter most of the lights that are beyond reach.
Normally when unconscious, SpongeBot's green lights are completely invulnerable to any damage as their hurt boxes vanish until the robot wakes up. New to Rehydrated, however, the robot's lights can now actually be damaged while knocked out as a way to speed up the overall fight, but this is normally unsafe as Robo-Plankton without a safe place to block his beams can interrupt and damage SpongeBob attempting to guide a Cruise Bubble.
SpongeBot SteelPants plays the role of the final boss in all games it appears in; the player must defeat the robot to complete the game.
In the original console versions and all Rehydrated versions, the player can fight SpongeBot SteelPants after earning 75 Golden Spatulas. After SpongeBob, Patrick, Sandy, Squidward, and Plankton all enter the Chum Bucket Lab, they discover SpongeBot and realize that Plankton was the original creator of the robots. Plankton tries to regain control of them, but Robo-Plankton (who claims to be SpongeBot's spouse) appears and initiates combat between SpongeBot and SpongeBob.
The player must destroy all nine green lights on SpongeBot's body, with the battle taking place on an arena surrounded by a large outer ditch via a central large bottom platform that contains bounce springs and underwear to refresh HP. The fight primarily takes place on the upper portion where a large amount of smaller floating platforms make up a perimeter around SpongeBot, which can be re-accessed through the aforementioned bounce springs since if SpongeBob falls down to the bottom arena at any time, the robot will restart its entire attack phase if SpongeBob bounces back up.
Upon having the power lights destroyed and ceasing its functions with its initial pair of arms falling off, SpongeBot then, later on, grows a pair of Anchor Arms and becomes even bigger. Robo-Plankton enters SpongeBot's head to repair it; SpongeBob follows and the player must shatter the power fuses inside and disable the robot's brain to shut it down as Robo-Plankton confronts him throughout his trek inside the SpongeBot's head.
In the Game Boy Advance version, SpongeBob enters the Chum Bucket and clears out most of the robots. Plankton says that he created SpongeBot to cook a Krabby Patty after the robots gave him the formula, but since they're running amok, he'll just steal the formula from the robots. After destroying the Duplicatotron ("Duplication" in this version), SpongeBob and Mystery fight SpongeBot itself, which hovers over the arena and throws bombs shaped like Krabby Patties. The player must use Mystery to grab these bombs and throw them at SpongeBot to damage it. After SpongeBot is hit with six bombs, it explodes.
The original console versions of Battle for Bikini Bottom contain assets for another phase of the fight against SpongeBot SteelPants where it has its Anchor Arms and wears a blue swimsuit along with having normal legs (along with being somewhat smaller). This phase of the fight briefly appeared in a trailer included with the special edition of Mario Kart: Double Dash!! where its eyes appear translucent instead of transparent, and with green irises instead of blue.
This phase crashes due to broken collision in his Anchor Arms, but replacing these broken files with blank files will fix the problem. There is no other way to damage him other than popping his Anchor Arms.
Both SpongeBob and Patrick would have been playable in this fight. SpongeBob appears running from the robot in the trailer, and Patrick would have been required to damage the robot's Anchor Arms by throwing objects at them. SpongeBot would have legs and shoes instead of its flame jets, and it would have been able to smash the ground with its Anchor Arms and create shockwaves by stomping on the ground. The boss has a variety of animations, each having their own variations whether or not either of its arms are popped.
SpongeBot's name was never stated in the original console versions of Battle for Bikini Bottom. Its name was given in the Game Boy Advance version and then confirmed in the achievement list for Rehydrated.
SpongeBot is the only robot boss in any version of Battle for Bikini Bottom where the character it resembles can fight it. Sandy cannot fight Robo-Sandy, Patrick cannot fight Robo-Patrick, Plankton is unplayable, and Squidward cannot directly fight Robo-Squidward (though players can use Squidward in Rehydrated's horde mode, which features Robo-Squidward).
Likewise, it is also the largest robot in the original game, barring Robo-Squidward in both the GBA version and in Rehydrated's horde mode.
SpongeBot is also one of the only bosses that can be damaged during nearly any period, as its green lights in several if not almost all situations have their hurt boxes active to be damaged (barring the time when SpongeBot is out-cold in the original console versions).
Originally, the entire first boss battle will also completely restart from the beginning due to the lack of cutscene phases compared to the other 2 robot bosses if SpongeBob dies from damage or going out of bounds. This is addressed in the remake to have SpongeBot's current HP amount retained if the player is defeated or goes out of bounds during the battle.
This is also one of the 3 boss fights in the original console versions that has its victory trigger hidden somewhere in the arena. A common way to beat the boss instantly is to reach its trigger high above one of the platforms via a high jump through exploiting the flipping platform's physics from both the SpongeBot's karate chop and KAH-RAH-TAE Cry, thus instantly skipping the battle and winning the first fight.
The interior of SpongeBot is much larger than the robot itself. SpongeBot does not actually increase in size after the first phase; the game uses optical illusions to make it appear that way.
Strangely enough, SpongeBot's power lights in both the Anchor Arms cutscenes and all the remake's cutscenes completely disappear on its person.
SpongeBot's taunt laugh sound is almost akin to the taunting laughter used several by of the common robot enemies.
While SpongeBot like several models in the console version of Battle for Bikini Bottom, in general, will always lock-on to the player's model in within a specific proximity, SpongeBot is somehow only able to do so when unconscious if SpongeBob is on the bottom portion of the arena, indicating that the robot is still semi-active during this portion.
Also during the phase, if Robo-Plankton is attacked while on the bottom arena (which causes SpongeBot to still be inactive until SpongeBob gets back up to the platform segment), the robot boss can be also awoken through triggering its taunt animation via SpongeBob receiving damage during this period.
SpongeBot also has an unused arm-shuffling-dance animation (which may have either been another idle or taunting animation) that does not appear in the final version of the original game.
Also during its unused Anchor Arms phase or when the player uses hacks or mods to reach Sandy next to Squidward and Patrick in the final version of the first boss fight, she has an unused pain animation when attacked that can only be seen during such segments.
The Xbox version of the fight somehow has two oddities:
One is that one of the power lights on the side of SpongeBot's head is somehow now placed properly on its model, and is somehow "jammed-in" to the side with one-half clipping through into its body.
Second is that the intro cutscene for the boss's initial battle only plays once per save file.