The Roboiler, also called the Robo-Boiler, is the second boss that appears in both versions of Sonic the Hedgehog Spinball. It is a rather bizarre chamber located in the highest room of Lava Powerhouse.
The Roboiler room contains four yellow Roboheads, each resembling Doctor Robotnik, the creator of the chamber. Above the corners of the chamber are two active steam jet machines located. In the 8-bit version of the game, however, the Roboiler room only has two Roboheads.
During the battle, each Robohead moves to one of five locations within the Robo-Boiler's chamber. These Roboheads vomit lava whenever Sonic hits them. To defeat the Roboiler, the player has to destroy all the Roboheads within the Roboiler by jumping into the Robo-Boiler and hitting them. Each Robohead takes five hits to be destroyed.
Whenever one of the Roboheads is destroyed, the remaining heads will temporarily vanish, leaving Sonic to tumble out of the Roboiler. The player then has to reenter the Robo-Boiler to hit the heads anew. In 8-bit version of the game, one of two Roboheads do not vanish after destroying another, making it possible for the player to destroy the second one at the same time. After destroying all the Roboheads, the Roboiler explodes, and the player has cleared the stage.
The most notable hazards in the room with the Roboiler are the jetsteam guarding the above corners of the chamber, which can block the player's if timing Sonic's Spin Jump wrong. Also, if the player lands on the closed hatch next to the jetstreams twice, it will open, which will result in Sonic falling down. Additionally, there are two targets on the bottom of the tank - hitting these will cause the drain plugs in the level to close.
When fighting the Roboiler, if the player falls into the drain on the left or right side of the room, Sonic will fall into the upper steam arena. If the player falls into the drain in the center, Sonic will fall down to the bottom of the level where he will emerge from a hole above a cauldron of boiling hot lava while hanging onto a chain above it for his dear life. To get out from there, the player has to utilize the chain hanging from the hole, where the player swing back and forth far enough and jump off at the right moment to escape. However, the chain is weak and will break if Sonic stays on it for too long as the game gives the player a countdown from five. This can only be done up to two times; the player will not be able to save themself falling into the center drain a third time which will result a loss of a life.
- In the 8-bit version of the game, each part of the boss rewards the player with a certain amount of points; hitting collision parts gives 2,000 points, each destroyed Robohead gives 5,000 points and after clearing the whole boss the player receives 1,000,000 points.
- Unlike the other rooms in the level, the drain plugs in the boss room do not open again after they have been closed.