Over time, Mephisto has lost the souls of Norrin Radd, Johnny Blaze, Ben Grimm, Franklin Richards, Susan Storm-Richards, Jean Grey-Summers, a full team of X-Men, Thor, Cynthia Von Doom, Bruce Banner, Jennifer Walters, Shalla Bal, Marlo Chandler-Jones, Kyle Richmond, Patsy Walker-Baxter-Hellstrom, Victor Von Doom, Danny Ketch, Barbara Morse-Barton, and presumably has lost many others.
Why he wants the souls of Peter Parker and his family, and to eliminate their marriage so badly is beyond my understanding...