During the battle between the Blue Devil and Shockwave, which you can read about somewhere else on this site (see if you can find it), Dan became the receptacle for an extremely destructive demon from Nebiros' dimension which had been hiding inside his trident. Well, that's not exactly true. In fact, the trident had simply become a conduit for mystical energy and the magic "coalesced into a demonic personality." But we won't quibble over minutiae. The demon had been biding its time, it said, until it was stong enough to emerge with such power. And to be sure, it did do a pretty quick number on both Shockwave and Green Lantern. Dan was no push-over, however, and he fought against the possession. Unfortunately, his will wasn't quite strong enough, but it bought his friends some time at least.
Finding the tattered remains of Dan's tuxedo, Norm pulled out Dan's little black book. Inside he found a number for Zatanna which rung a phone at the Justice League Satellite. Hearing the bad news, Zatanna rushed to the scene as fast as the wind could carry her. She felt guilty at having allowed Dan to keep the trident without assuming something such as this might happen. When she arrived, however, even Zatanna couldn't do very much. But she did help Dan get a grip on himself and force the demon from his body and into the trident where it manifested itself as some sort of fire creature. Assuming that this demon, having come from Nebiros' dimesion, might be vulnerable to the same stuff as Nebiros (i.e. water and other wet things), Zatanna gave Dan the key to beating it. Forcing it into the movie theater, he doused the creature in Kwikee Kola.
After that, it flew around a bit searching for a new host, briefly settling on Jock Verner, before quickly dissipating, no longer having the mystical energy to remain a part of this dimension.