But he would need to be in the World Stone Chamber to do that, and it doesn't actually grant him power, if I remember correctly, since he isn't tied to it. He was only using it to break the barriers between the worlds (or atleast that's what the in-game content suggested.)
In mythology, Mephisto, or Mephistopheles had many children spawned from the pairing of evils, the pairing of heavens and evils, as well as the spawn of incubi. Mephisto controls the supposed portals the the gates of the underworlds as well as assigned to collect souls promised to the Lord Lucifer himself represented as "Diablo". This would suggest that Mephisto was the strongest in battle due to the pure sociopathy of his personality. In many stories the Devil (Diablo) makes well on promises and deals that he makes with mortals as well as those from the angels burrow, however Mephisto lives on deception destruction and sadism.
Mephisto would win that fight.
Now, Baal, or Bael was said to be the first lieutenant to the Lord Diablo with 66 legions of the spawn of afterlived souls and Diablo himself. Some dispute that he is King of Hell in the east. By representing Hell as a circle Dante Allighiri dismissed the idea and brought Baels representation under false assumptions into the sixth layer of Hell, Lucifer or Diablo of course reserved in the seventh layer, suggesting that Diablo kept Bael under his thumb, supporting the theory that not only would Mephisto kick Diablo's ass, but he could wipe his ass with the afterlifeless Bael and discard him like a cigarette.
You forget that in that very mythology, Lucifer is the one who led the revolt against heaven, and is the Chief Prince of Demons (fallen angels)... Mephistopheles is not cannonitically considered a Jewish demon. His popularity mostly came about with the play Faust.
Like Phrozen said, Diablo is not Satan. Diablo isn't even remotely like Satan, since he's supposed to be an Angel of Light (after the Fall of Lucifer, he's considered the Angel of False-Light, or Lies, or Prince of Lies.) Diablo is a big red dragon with a Spanish name.
Um, they were united, I believe. Didn't the Horadrim fight them near Lut Gholein and then imprison them? Then from there their soul stones were split up- one for Mephisto, which was kept at the bottom of the tower of Travincal, Baal's that was sealed in Tal Rasha's chamber, and Diablo's that was unaccounted for location-wise (before Diablo was released), but was never-the-less summoned up from the bowels of Tristram.
What I've said was that why would Diablo after freeing Baal travel into Kurast to visit Mephisto, this being at the end of Act 2 cinematic. Yes they've been in Kurast but the question is why?
Diablo and Baal both went to Kurast, specifically to the bottom of Travincal's tower (Mephisto's Durance), and met with Mephisto there to open the gate to Hell, which they had been banished from for some time.
You forget that in that very mythology, Lucifer is the one who led the revolt against heaven, and is the Chief Prince of Demons (fallen angels)... Mephistopheles is not cannonitically considered a Jewish demon. His popularity mostly came about with the play Faust.
Like Phrozen said, Diablo is not Satan. Diablo isn't even remotely like Satan, since he's supposed to be an Angel of Light (after the Fall of Lucifer, he's considered the Angel of False-Light, or Lies, or Prince of Lies.) Diablo is a big red dragon with a Spanish name.
Diablo and Baal both went to Kurast, specifically to the bottom of Travincal's tower (Mephisto's Durance), and met with Mephisto there to open the gate to Hell, which they had been banished from for some time.