Mootonium is a green-glowing and radioactive liquid substance. Possessing extremely dangerous and explosive properties, it needs to be kept at low temperatures. Otherwise, it will become unstable and explode.
Due to its volatile nature, Mootonium makes an excellent resource for nuclear-based weapons. For example, filling a robot as large as Cowbot with Mootonium could create an explosion powerful enough to vaporize everything within a twenty-mile radius.
A large amount of Mootonium was used by Dr. Eggman to fill his creation Cowbot, which he used against Team Sonic. This created a machine that Team Sonic could not destroy without the Mootonium exploding and taking them with it. As such, Team Sonic resorted to reprograming Cowbot, and later gunk it up when it went after Eggman.
During spring clearing, Dr. Eggman forgot to take half a dozen barrels of Mootonium out of his lair's basement. Fortunately, the lair's air conditioning kept the basement cool enough for the Mootonium to remain stable. When Amy and Tails later got stuck in the basement, they discovered the barrels of Mootonium, which they tried to keep cool when the air conditioning got turned off. The danger the Mootonium posed provided the incentive for everyone in the lair to escape, which they did just before the Mootonium exploded and destroyed the lair.
- Mootonium's name is a reference to the real-life element plutonium.