Despite being an insane monster, a couple of scientists theorized that there was an intelligence in the creature that went unseen. They began work on a way to decrease the creature's hunger and corruption, but their research was cut short when Iiji demanded Jaysiph be locked away and forgotten. Such an imperfect creature would be next to useless to her.
But she kept Jaysiph alive, feeding him just enough food and majicka to keep him going, just in case she had need for such a powerful creature. Even if an entire army appeared outside her facility, they would need the power of the gods to stand up to this terrible creation of science.
Jaysiph does not do very much on his own, instead COUNTERING every action made against him. The scientists used this fact to work on a safety mechanism for taking him down should the need arise. They created a special solution that would nullify all his majicka, causing him to die from his hunger within minutes of being injected. Unfortunately, they couldn't perfect the formula, and their test subjects would always get their majicka back after a few moments.
Unfortunately, the non-majibeast scientists died either of old age, attacks from other majibeasts, or by making Iiji angry. Research on Jaysiph was brought to an end and he rested in his cage waiting for the day he'd break free and find an endless fount of majicka to consume.