The Diabolique is a fictional character in the prime reality of the Marvel universe of Marvel Comics. Which was created in 1993 by Chris Cooper and Rurik Tyler, first appearing in issue #9 of the 1st volume of Darkhold: Pages from the Book of Sins.
Diabolique is a demon/human hybrid that has a ties to both the Darkhold and the Cult of the Darkhold. Appears as a 6 year old child, but is vastly older though she acts as a bratty child, a twisted sadistic one. She is constantly seeking out surrogate parents, who she later kills when she decides to move on to a new set of parents.
The demonic child possesses a number of magical powers. She gains the form of those she kills and their bodies and souls are fused into an entity called Playmate. Which at's smallest is the size of a mouse which can grow to massive size and slaughters everything that's in its path, growing in power as the number of victims that it absorbs increase. It smothers, renders, strangles, and engulfs its victims. The entity projects heads, tentacles, and limbs with claws and teeth. Diabolique's power increases as the power of the Playmate grow, but if it's destroyed she is temporarily made powerless.
At full power, she can open dimensional portals, manipulate and absorb hellfire, tear apart victims, mentally control others, and practice sympathetic magic (e.g. voodoo dolls). She uses a spider called Zoroaster, which is the size of a small tarantula and she treats as a pet (Zoro). It is immune to hellfire, possesses superhuman strength, is able to regenerate it's limbs, and can increase its size to that of an automobile.