HOW?? Prep wasn't super helpful to Pym as a member of the Avengers vs Mephisto in any of their encounters. Daimon has manipulated Mephisto into a weak position before and had him, Satanish, and Dormammu fighting each other. He's had his father Satan on the ropes a few times and in Defenders (105 IIRC) it was shown that Mephisto is simply ONE of the aspects of Satan. http://s1232.photobucket.com/user/b...sort=3&o=83
As much as I hate ABC logic, Pym with prep and very powerful team mates has failed to defeat on several occasions someone that Hellstrom has defeated as often as Pym and the Avengers have failed. How exactly does that give you a win with prep??? I'll assume that your planning on throwing up the scans of where Pym used science to counter the magic of Loki. Loki and Asguardian magic =</= Hell lord magic and hell fire. Loki is a BLOODy good mage and very creative. he's one of the few who uses magic combined with science (or magic to use, create science or vise versa). Loki would not fair well vs Hellstrom, the conventions he relies on so often in his adversaries simply aren't there to take advantage off.
Pym negated an energy signal (Asguardian magics) and has used his shrinking powers to deal with explosions (shrinking them as fast as they expand) either is a solid counter is a solid counter to Hellfire and Pym's robotics could help win this.