I am waiting and waiting and waiting for #140, and it hasn't come yet. I really want to read it, because it has Mephistopheles on the cover. Does Mephistopheles actually appear inside?
Sadly, the archdevil himself appears only on the cover; but the cover, by Howard Lyon, is glorious!
The adventure "Heart of Hellfire Mountain," by Dave Olson, places a 20th-level adventuring party in the fascinating position of allying themselves with a fire giant king. The king needs aid defending his kingdom against Mephistopheles'a minions, who have erected a volcanic temple nearby and plan to crush the fire giants first in their campaign of earthly domination. The archdevil's minions are exceptional adversaries in their own right, and further empowered by an artifact that carries the archdevil's powers to the material plane, but Mephistopheles himself does not make an immediate personal appearance.
To say more might undermine the joy of reading the adventure!
Yes, sadly- Every time a demon lord or archdevil has appeared on the cover, their appearance has not been made in the issue itself.
However... I can't think of a time when the adventure in such an issue wasn't awesome. Graz'zt on the cover? Fiend's Embrace. Demogorgon on the cover? Lost Temple of Demogorgon. Juiblex on the cover? Caverns of the Ooze Lord, or whatever it was called. I forget right now, but it was an excellent adventure.
And here, this delightful near-epic romp, with a wonderful cover featureing Mephistopheles.
If you're still dissapointed by this, you can always work up an aspect for the PCs to fight. I'm sure the Fiendish Codecies have scads of info on aspects.