Mephisto draws his power from the number of human souls enslaved within his realm. These souls can only be obtained via consent, so Mephisto has made numerous deals and bargains with mortals with their souls as collateral. Without fail, there is always a catch or loophole Mephisto exploits in order to trap the soul in question. For instance, Mephisto once made a deal with young stunt rider Johnny Blaze to cure Blaze's father of cancer. Mephisto cured the disease, but did not lift a finger to help when the elder Blaze died in a stunt gone wrong. Thus, Mephisto bound the demon Zarathos to Blaze, creating the Ghost Rider. Mephisto also takes great joy in attempting to lure especially pure souls like Thor or the Silver Surfer into sinning.
Battle vs Lich King (by CuchulainSetanta)Edit
In Mephisto's palace in the Stygian Deeps, Mephisto is angered to learn that an entity known as the Lich King is taking souls that Mephisto could use for his own. Transporting himself to Icecrown, Mephisto arrives right in front of the Frozen Throne. Seeing this threat to his rule, the Lich King rises, unveiling Frostmourne and summoning a legion of undead to attack the intruder.
With a simple wave, Mephisto blasts a wave of hellfire at the Scourge forces, incinerating them. The Lich King is surprised, but steps down to meet the hell-lord in combat. He thrusts forward with Frostmourne, but Mephisto evades by teleporting behind him. Gathering another wave of hellfire, Mephisto blasts the Lich King, knocking him to his feet.
Mephisto approaches the fallen King, but is stopped in his tracks when the Lord of the Dead summons a blizzard, buffeting Mephisto with hurricane-force winds. Shouting in fury, Mephisto blasts the blizzard back with a burst of hellfire, then leaps for the King. Readying himself, the Lich King catches Mephisto on his blade, causing the demon to explode in a shower of hellfire.
The Lich King laughs, walking back to his Throne, only to be knocked to his feet when the Citadel shakes violently. Getting back up, the King walks to the edge, looks down, and sees Mephisto down below, sucking Icecrown Citadel into a portal down to Hell; the Mephisto who had been fighting this entire time was just an illusion. Another tremor sends the Lich King plummeting down into the inferno, with Mephisto catching Frostmourne as it hurtles past. Mephisto absorbs the countless souls within the blade, cackles, and then disappears to torture his new prisoner.