Dr. Strange: Dead Cat Syndrome
From DR< STRANGE #49. Villains do nasty things. Killing a new character's cat in order to disguise yourself as said dead cat is EXTRA nasty.
Dr. Strange received a phone call from Morganna Blessing, who would go on to become an important supporting character in the series.
Basically, Morganna realizes there's more to Dr. Strange than meets the eye and calls him up. (Strange is in the Yellow Pages?) Mordo is able to eavesdrop from a "point in infinity" and sees Morganna as a way of getting back to Earth and defeating Strange once and for all.
Pet murder. Now that's low.
Mordo died in an above-average Strange story by J.M. DeMatteis, which I may post. He somehow came back in AMAZING SPIDER-MAN #500, although that was never fully explained. If he will appear in the new Dr. Strange or Dr. Voodoo series, I hope some reasoning behind his return.