The Skullgirl is a powerful and pale female being that is the result of an "impure" lady making a wish using the Skull Heart which later merges with the user. They were supposed to be mindless servants of the Trinity, with the task of destroying the world, but Marie proved otherwise with her strong heart.
The Skullgirl have a skull and bone motif to her outfit, pale hair and skin, red eyes with skull irises with dark lines under them and The Skull Heart will be placed in her exposed back surrounded by blue flames. In some cases, other parts of the Skullgirl's body will become boney and skeletal, mostly the hands and arms. Judging from the basic appearance of Selene Contiello and Marie, the spine and almost all of a Skullgirl's organs are removed or missing, as the Skull Heart nests itself inside their backs, and parts of Marie's ribcage is exposed with no visible internals at all.
The Skullgirl gets her power from the Trinity. As shown by Marie, she can make skulls float so she can use them as projectiles. Skullgirls can control the undead, as in the case of Selene Contiello, Squigly's mother. Squigly was supposed to be a part of her army but her parasite Leviathan helps her keep her own mind. The only attacks that Marie demonstrated that involves no skulls at all are where she uses a giant, masculine figure that is always behind her (only used in the 2nd and 3rd forms) to physically assault her foes, and her vacuum cleaner-scythe (the vacuum cleaner was made of bones but has no visible skulls on it).
- Filia (Filia story only)
- Painwheel (Painwheel story only)
- Valentine (Valentine story only)
- Parasoul (Parasoul story only)
- Queen Nancy Renoir
- Selene Continello
- The giant female, masculine figure may be the figure of the Great Mother herself.
- The process of transforming into a Skullgirl is long and painful, as shown in Filia's ending.
- Skullgirls are, literally (and strictly), girls, so its is unknown what will happen should a male character make a wish with the Skullheart.