Carlos Pacheco and Rafael Marin begin a fairly long run on this series with a two-parter about Diablo.
The team receives a special delivery package with a magic mirror that, when opened, unleashes demons that try to pull them in through the mirror/portal.
Diablo then passes through the mirror to the Baxter Building and overpowers Thing and Human Torch, and then unleashes an army of elementals on New York City.
Issue #36 has NYPD Code Blue, Daredevil and Spider-Man guest starring to help fight the elementals while Reed uses science to defeat Diablo.
If you’re a Diablo fan, there are some things in this story that flesh out his origin—and it is implied that he has immortality based on some kind of connection to Dracula.
As for subplots: While Thing and Johnny are fighting Mr. D., Sue and Reed are working with lawyers (Foggy Neston and Jeryn Hogarth) to help Fantastic Four Inc. get out of debt. (A meta-note: Marvel itself was working with lawyer on the same problem in 2000.) In addition to financial woes, they’re basically homeless since the Thunderbolts commandeered the Baxter Building, then destroyed it, while the FF were stuck in the post-Onslaught pocket universe. There’s also a scene showing Noah Baxter, who designed the Baxter Building, heading to New York to help.