Retro-Metabolism (Captain Scarlet and the Mysterons).
The user is immortal in the sense that when they do die, they won't stay dead. This could be the result of instant resurrection, being reborn, transferring one's mind/soul into a clone, etc. Unlike other forms of immortality they can still die from any cause, like physical trauma, disease or simply aging, but the user will always come back to life.
The most famous quality of Ajins (Ajin: Demi-Human) is that they never stay dead.
Humanoid Cylons (Battlestar Galactica) continuously resurrect in new bodies upon their current bodies' deaths.
After being killed and reconstructed by the Mysterons, Captain Scarlet (Captain Scarlet and the Mysterons) gained the Mysteron power of "Retrometabolism" which allows him to heal from serious injuries and return from death.
Mitchell Shelley/Resurrection Man's (DC Comics) power is the ability to die and resurrect with a random power, usually somehow associated with his death.
After being killed by the Daleks and then resurrected by Rose Tyler, Captain Jack Harkness (Doctor Who) gained the ability to come back from death
Henry Morgan (Forever)
As the central hive mind of the parasitic Flood, the Gravemind (Halo) can keep resurrecting itself ad infinitum as long as even a single Flood spore still exists to infect other creatures.
After becoming a spirit, if Victor's (Hatchet) body is somehow destroyed or "killed", he'll come back because he has to repeat the night he died for eternity until he finds his father.
Chucky (Child's Play)
Jason Voorhees (Friday the 13th film series)
Freddy Krueger (A Nightmare on Elm Street series)
Matthew Cordell (Maniac Cop Trilogy)
Phantom (Marchen Awakens Romance) cannot stay dead as long as he has the Zombie Tattoo. It’ll take a few years, but Phantom will eventually be resurrected.
Mr. Immortal (Marvel Comics) is a Homo Supreme, having evolved beyond death, he will always come back to life no matter how many times he is killed
Nathan Young (Misfits) will always come back to life upon death, no matter how long it takes.
Geras (Mortal Kombat 11) is a living fixed point in time. Every time he's killed, he will eventually return to life, stronger than before.
Upon death, Ozma’s (RWBY) soul merges with a like-minded person in a process of reincarnation.
Whenever SCP-076-2 - "Able" (SCP Foundation) is killed, his corpse disintegrates and his body reforms inside the stone cube designated SCP-076-1, making him essentially immortal.
Sekiro (Sekiro: Shadows Die Twice) has the ability to resurrect himself an infinite amount of times thanks to his master, Kuro, the Divine Heir, granting him the power of the Dragon's Heritage.
Hans Moleman (The Simpsons) has a running gag of him being killed in various accidents only to come back alive and unharmed.
Tomie Kawakami's (Tomie) healing factor can not only bring her back from death...
...but any part of her has the chance of turning into an entirely new version of her.
Snow White (Valkyrie Crusade) is an absolute immortal in that while she can die, she never can stay dead, and will always come back to life, no matter how she dies.