However, when he was released in 666, Diabolico found that his era of rule had ended, for he was now an equal to Empress Bansheera. He was the key who helped Bansheera establish her grand Palace within the Alasdair Kingdom, and also commanded all of the demon generals and soldiers against the likes of Zordon and Ninjor and helped all of Unagi's forces gain the upper hand in war. When Melladon's life force energy wave spread through, Unagi's forces were neutralized, and Diabolico lost his bodily form, trapping him in a weakened spectral form which allowed the Warlock to easily seal him again in the Tomb of Forever in that same year, where he would remain for the next several centuries.

Unagi Garenth himself would release the demons from the Tomb in 2057, though it would take Diabolico until 2238 to gain enough strength to obtain a physical form. Diabolico, a master of strategy, observed his present enemy, Lightspeed, from afar. He would formulate the plan to steal Lightspeed's Titanium Morpher and hand it to a human of his choosing in 2252. This human would be three-year old Ryan Mitchell.

After kidnapping Ryan, Diabolico infused the child with an incredible amount of his own demonic strength, ensuring that Ryan's body would be strong enough to handle the power of the Titanium Morpher. Afterwards, Ryan was trained in Diabolico's ways, learning the arts of darkness and desynthesicing him from guilt, shame, and pity. And in 2269, the Titanium Ranger was unleashed against Lightspeed.

Diabolico's plan resulted in the deaths of all five Lightspeed Rangers, and the destruction of Lightspeed itself. However, it was Wesley Collins who managed to completely seal off the demons from the Earth before their armies could once again march the world.

After that, Unagi had ordered both Bansheera and Diabolico to keep low profiles until the inevitable Monarch Invasion of 3017, where Diabolico had a helping hand in the conquering of KO-35 alongside Emperor Zedd.