Vengeful spirit

Defined across sources as the spirit of a deceased person bound to the living world by an unresolved grievance, typically arising from a cruel, unnatural, or unjust death or from not having been given a proper funeral; the spirit's return is motivated by a desire for revenge or redress when human institutions or rites have failed (Wikipedia; Wikidata).

The provided sources give no consistent or canonical physical description. Accounts treat the vengeful spirit as the returned dead with variable portrayal depending on cultural or narrative context; descriptions range from 'unhappy ghost' following improper burial to fictionally individualized manifestations in popular culture. No single traditional form is attested in the supplied materials.

Sources consistently describe the core ability of returning from the afterlife to interact with the living in order to seek revenge for an unjust death (Wikipedia; Wikidata). Popular-culture materials illustrate that such spirits may harm or target perceived offenders and that their judgments can be distorted after death (Supernatural wiki). The supplied materials do not enumerate a fixed catalogue of powers (possession, materialization, sickness, etc.) but do support that a vengeful spirit can persist and act in the living world until its grievance is addressed.