Classic. Never aging, never dying, no illness. (Boring answer.)
Time loop. Same day, week, year, whatever, over and over. You stay then.
Vampiric. Never aging, but you are dead.
Norse god. You’re immortal as long as you eat a specific thing (like the apples)
Phoenix. Forever reborn, never reincarnated. Same life, many births.
Reincarnation. Many lives, many births. Same souls.
Undead. You can’t die; you already have.
Spirit. Similar to undead, but you have no corporeal form.
Regeneration. You can die, but you won’t stay there.
Cryonic freezing. “Walt Disney” style. You get frozen but can come back.
Uploaded to a computer. Like Elon Musk is planning.
Remembered. Oh you fucker. Yeah sure, you’re immortal because you have a legacy.