This power is not full immunity; the user can still be harmed, and potentially killed, by such things if enough is used.
Scarecrow (Batman: Arkham Knight)
Superboy (DC Comics)
Kain (Legacy of Kain)
Wolverine (Marvel Comics)
Type 2 Plagas (Resident Evil)
Quint Lane (Underworld)
Due to his prolonged exposure to it, Scarecrow (Batman: Arkham Knight) has built up a partial immunity to his own fear toxin, though he was still affected when Batman injected him with several vials of it.
As a dhampir, Rayne (BloodRayne) is more resistant to sunlight and water than pure vampires.
As a human-Kryptonian hybrid, Superboy (DC Comics) is more resistant to Kryptonite than pureblood Kryptonians.
Kain (Legacy of Kain) possesses an immunity to certain forms of water, such as rain and snow, but cannot survive being immersed in large bodies of it.
The enhanced Type 2 Las Plagas (Resident Evil) are resistant to sunlight and other forms of bright light, though very intense light, such as flash grenades, still harms them.
Due to his Regenerative Healing Factor, Wolverine (Marvel Comics) is highly resistant to diseases, drugs, and toxins, though he can still suffer the immediate effects of such substances in massive quantities.