The user either is or can become a half-mutant. Compared to mainstream deviants, they have mutations that made them lose their trace of what race they are halfway, yet they still have their consciousness and rationality intact, and this is what makes them stronger than ordinary mutants.
Half-Deviants still have instability in their DNA, but only to a much lesser extent.
Albert Wesker (Capcom/Resident Evil 5); when infected with Uroboros
Teresa/Talon (DC Animated Universe/Static Shock)
Turanga Leela-Fry (Futurama)
Gido (Marchen Awakens Romance)
Deviant/Mutant Hybrids (Marvel Comics/X-Men)
Human/Deviant Hybrids (Marvel Comics/X-men)
Maelstrom (Marvel Comics)
Herbert Landon (Marvel Comics/Spider-Man: The Animated Series)
Curtis Miller (Resident Evil: Degeneration); 1stStage
William Birkin (Resident Evil Series); 1st Stage
J’avos (Resident Evil 6)
Hybrids (System Shock 2)
Turanga Leela-Fry (Futurama) is relatively speaking, not as mutated compared to ordinary Mutants, presumably being born between the union of a Human and a Mutant more or less.
Half of Gido's (Marchen Awakens Romance) body was horrifically mutated by Chimera to punish her boyfriend Ian for disobeying orders.
Maelstrom (Marvel Comics) is a hybrid of two different Human subspecies, namely Deviants and Inhumans.
Being former Humans from being injected with the Chrysalid Virus into the bloodstream, J’avos (Resident Evil 6) are normally in a half-mutated state at first, though they can mutate themselves further for more power, especially in reaction to injury.
In the process of being infected with Grubs, they will slowly turn the Humans into Hybrids (System Shock 2). Unlike the Rumblers and Psi Reavers that are full-on Mutants, the Hybrids only meet the way of mutation half-way until the later stages. Physiology wise, their voices have also changed, specifically reverberating and low-pitched.
Mut-Orgs (Power Rangers Time Force) are half-mutant, half-Org.