Nice copy from a private collection

"By My Powers Shall I Be Vanquished!" Part 3 of 3. Guest-starring the Sub-Mariner. Script by Denny O'Neil. Art by John Romita Jr.  and Jim Mooney.  In a diabolical twist of fate, the Wizard transfers Spider-Man's spider-sense into the mind of the Sub-Mariner! The web-slinger's sudden loss and Prince Namor's sudden gain make them easy prey for the Frightful Four! After taking a beating, the two heroes go their separate ways to lick their wounds! Hours later they rendezvous at the Baxter Building to reverse the Wizard's experiment! And then it's time for payback! The Spectacular Spider-Man and the Avenging Son vs. the Frightful Four! Imperious Rex! Cameo appearances by the Invisible Girl, Mr. Fantastic, and the Thing. Cover price $0.50.