The second appearance of the Frightful Four is often overlooked in light of their subsequent and now classic battle with their counterparts in the Fantastic Four, a final battle which had the evil FF on the brink of victory but ended in the dissolution of the original lineup of this classic team of villains for all time. Yet that second meeting was a key encounter in solidifying their threat level and cementing their status as a force to be reckoned with, however briefly. Once Madam Medusa was no longer a part of their operations, the Frightful Four had the wind taken out of its sails, going through one replacement member after another but never reclaiming its glory days. Perhaps that's one reason why its five appearances (if you're counting their brief reunions in Europe and Whisper Hill) are remembered above all others.
Yet as much as their third battle with the FF assured their standing as one of the most ruthless and outstanding villain groups in comics, it was their second battle, at an abandoned Pacific atoll where the Wizard had prepared a carefully laid trap for their enemies, that saw them follow up on their first encounter with the FF--a fight which ended in a stalemate but would lead to their total triumph just two issues later, one that even had the issue's cover declaring their victory for all to see.
Can no one stop the Frightful Four??
(I guess we know who it won't be!)