Chaos Shadow

From the Sonic News Network, the Sonic Wiki

Shadow the Hedgehog can cause this temporary energized state by removing the rings he wears around his wrists. This creates an incredible surge of Chaos Energy, but causes exhaustion after the energy is released.

Shadow used this in Sonic X after fighting the Finalhazard alongside Sonic. He removed the rings and combined his Super transformation with his Chaos power to increase the potency of his Chaos Control. In Sonic the Hedgehog (2006) Shadow used this to eliminate the copies Mephiles made of himself. When he took off his rings, an explosion occured from the surge of energy, giving Shadow increased power and a yellow aura which covered him as well, Rouge, and E-123 Omega.

Interesting to note that although Shadow supposedly becomes exhausted after releasing his rings, in Sonic the Hedgehog (2006), Shadow did not seem to be after releasing his rings to destroy said army of Mephiles clones. Whereas in Sonic X, following his fight with Finalhazard, his exhaustion overwhelmed him, causing him to fall to Earth. Because of this, he was presumed "dead" until later episodes.