There are essentially six levels of immortality:

• Ageless
  
• Biological-Only
  
• Basic
  
• Full
  
• Near-Total
  
• Total

There can be atypicalities with any of these levels wher ethe fundamentals of the minimum requirements are ment but there is some flaw or achillies heel.

The six levels are defined below. With power minimums defined in for tabletop RPGs Mutants & Masterminds (M&M) 3rd Edition, Big Eyes Small Mouth (BESM) 4th Edition, and Generic Universal Roelplaying System (GURPS) 4th Edition.

The person just simply stops aging, but can die any other way including radiation accumulation, pandemic, slow poisoning, cancer, etc….

• M&M Minimum:
  
  • Immunity to aging, innate -- 2pp
• BESM Minimum:
  
  • Resilient: Aging - Complete -- 1(2) 4pts
• GURPS Minimum:
  
  • Unaging -- [15]
• Examples:
  
  • Crusader Kings 3 Immortality mods that don't set the disease immunity character flag

The person stops aging and will never die from any non-weaponized natural cause - disease, poison, age related disorders, accumulated radiation exposure. Injury and weaponized poisons/radiation (chemical weapons, lethal radiation exposure) will still hurt and kill the immortal.

• M&M Minimum:
  
  • Immunity to aging, poison, disease, environmental radiation, innate -- 5pp
    
  • (optional) For limb regrowth: Regeneration 1 persistent innate -- 3pp
    
• BESM Minimum:
  
  • Resilient: Aging, Disease - Complete -- [2(4) 8]
    
  • Resilient: Radiation, ingested poison, airborne toxins - only to prevent death, lasting disability, long-term health effects -- [3 6]
    
  • (optional) For limb regrowth: Regeneration 3 health -- [3 15]
    
• GURPS Minimum:
  
  • Unaging -- [15]
    
  • Resistant - Disease, Poison - Immune -- [20]
    
  • (optional) For limb regrowth: Regrowth -- [40]
    
• Examples:
  
  • Lord of the Rings elves (explicit)
    
  • TinTin (implicit)
    
  • Peter Pan and other inhabitants of Neverland (as long as they remain in neverland)
    
  • Nightcrawler (X-Men)
    
  • The Thing (Marvel comics, Fantastic Four) - only when in the form of The Thing, but can only be in human form one day per year.
    
  • Crusader Kings 3 Immortality mods that do set the disease immunity character flag
    

As biological immortality but also cannot die from injury, but bodily destruction will kill the immortal -- beheading, getting blown up, getting spaced out of airlock, getting incinerated, getting completely mulched into ground meat or chunked into little pieces. Most of the head and a notable portion of torso must be intact to not die. Typically a resurrective immortality with a come-back time sometime between an hour to a day. Restoration will often occur even in non-life-sustaining areas such as drowning, poison gas. Lost limbs and non-life-vital body parts will not come back without some form of regeneration or regrowth.

• M&M Minimum:
  
  • Immunity to aging, poison, disease, environmental radiation, permanent, innate, no limits or sources-- 5pp
    
  • Immortality 5 (limit head & significant part of torso must be intact) innate -- 11pp
    
  • (recommended) For limb regrowth: Regeneration 1 persistent innate -- 3pp
    
• BESM Minimum:
  
  • Reincarnation 3 (stopped by destruction of head or entire torso) -- [3 6]
    
  • Resilient: Aging, Disease - Complete -- [2(4) 8]
    
  • Resilient: Radiation, ingested poison, airborne toxins - only to prevent death, lasting disability, long-term health effects -- [3 6]
    
  • (recommended) For limb regrowth: Regeneration 3 health -- [3 15]
    
• GURPS Minimum:
  
  • Unkillable 2 [Limit: 'Die' by normal rules instead of only at -10*HP -10%, Achilles Heal - Head and portion of spinal cord must be reasonably intact, -50%) -- [40]
    
  • Regeneration - Regular (1 HP per hour; Limit: Only when 'dead', -60%, Extras: Heals Radiation +40%) -- [20]
    
  • Unaging -- [15]
    
  • Resistant - Disease, Poison - Immune -- [20]
    
  • (recommended) For limb regrowth: Regrowth -- [40]
    
• Examples:
  
  • Highlander (can’t loose head)
    
  • Wolverine (Marvel comics X-Men)
    

As basic immortality but can not die even with total body destruction as long as at least one cell remains in its original chemical state. Complete combustion, disintegration, or conversion to energy will kill the immortal. Sometimes resurrective with a come-back time of a minute to an hour.

• M&M Minimum:
  
  • Immunity to aging, poison, disease, environmental radiation, permanent, innate, no limits or sources -- 5pp
    
  • Immortality 10 (1 hour) permanent, innate, no limits or sources -- 21pp
    
  • For limb regrowth: Regeneration 1 persistent innate -- 3pp
    
• BESM Minimum:
  
  • Reincarnation 5 (difficult to stop) [5(6) 12]
    
  • Resilient: Aging, Disease - Complete -- [2(4) 8]
    
  • Resilient: Radiation, ingested poison, airborne toxins - only to prevent death, lasting disability, long-term health effects -- [3 6]
    
  • For limb regrowth: Regeneration 3 health -- [3 15]
    
• GURPS Minimum:
  
  • Unkillable 2 [Limit: 'Die' by normal rules instead of only at -10*HP -10%) -- [90]
    
  • Regeneration - Fast (1 HP per minute; Limit: Only when 'dead', -60%, Extras: Heals Radiation +40%) -- [40]
    
  • Unaging -- [15]
    
  • Resistant - Disease, Poison - Immune -- [20]
    
  • For limb regrowth: Regrowth -- [40]
    
• Examples:
  
  • Deadpool (Marvel comics)
    

As full immortality, but cannot die even with complete combustion, disintegration, or conversion to energy. Resurrection time of a minute or less. Often has extreme levels of injury tolerance and regeneration. Resurrection may be halted if under constant state of destruction (constant incineration etc..). Imprisonment is still possible.

• M&M Minimum:
  
  • Immunity to aging, poison, disease, environmental radiation, permanent, innate, no limits or sources -- 5pp
    
  • Immortality 15 (extra: no remains required at all), permanent, innate -- 46pp
    
  • For limb regrowth: Regeneration 1 persistent innate -- 3pp
    
• BESM Minimum:
  
  • Reincarnation 6 (difficult to stop) [6(7) 14]
    
  • Resilient: Aging, Disease - Complete -- [2(4) 8]
    
  • Resilient: Radiation, ingested poison, airborne toxins - only to prevent death, lasting disability, long-term health effects -- [3 6]
    
  • For limb regrowth: Regeneration 3 health -- [3 15]
    
• GURPS Minimum:
  
  • Unkillable 2 [Limit: 'Die' by normal rules instead of only at -10*HP -10%) -- [90]
    
  • Regeneration - Very Fast (1 HP per second; Limit: Only when 'dead', -60%, Extras: Heals Radiation +40%) -- [80]
    
  • Unaging -- [15]
    
  • Resistant - Disease, Poison - Immune -- [20]
    
  • For limb regrowth: Regrowth -- [40]
    
• Examples:
  
  • Jean Grey (Marvel comics X-Men, as Phoenix Force host)
    
  • Netflix Japanese Anime series Ajin Demi-Human
    
  • Mr. Immortal (Marvel Comics)
    

The immortal cannot die, period. Even if disintegrated or completely vaporized or ashified. You just don’t die, period. Resurrection is usually not required - you just don’t die. Regeneration is rapid. Recovery / re-materialization is usually near instant - a second to a minute - if resurrection is needed. Resurrection may be halted if under constant state of destruction (constant incineration etc..). Imprisonment may still possible.

• M&M Minimum:
  
  • Regeneration 10 persistent, permanent, innate (innate & only applies on first rank, for regrowth) -- 21pp
    
  • immunity to all fortitude effects permanent, innate (innate only applies to ageless aspects) -- 30pp
    
  • Immortality 20 (extra: no remains required at all), permanent, innate -- 61pp
    
• BESM Minimum:
  
  • Reincarnation 7 (enhancement: difficult to stop) -- [7(8) 16]
    
  • Regeneration 6 Health -- [6 30]
    
  • Resilient: Aging, Disease, Ingested Poison, Inhaled Toxins, Radiation, Sustenance, Intense heat, Intense Cold, Low pressure, Lack of air - All complete -- [10(20) 40]
    
  • Immunity 10 (all forms of injury) -- [10 30]
    
• GURPS Minimum:
  
  • Unkillable 2 -- [100]
    
  • Regeneration - Very Fast (Extras: Heals Radiation +40%) -- [140]
    
  • Unaging -- [15]
    
  • Resistant - All metabolic hazards - Immune -- [30]
    
  • Doesn't Breathe -- [20]
    
  • Doesn't Eat or Drink -- [10]
    
  • Pressure Support 3 -- [15]
    
  • Sealed -- [15]
    
  • Vacuum Support -- [5]
    
  • Radiation Tolerance PF 10000 -- [45]
    
  • Temperature Tolerance 80 (assuming HT 10, -415 to 440) -- [80]
    
  • Injury Tolerance (Unliving) -- [20]
    
• Examples:
  
  • None
    

Has core of biological, basic, full, or total immortality, but has peculiarities, such as abnormally long revival time (insufficient rank in immortality), need of a catalyst / source, etc.. Often label is augmented with level of immortality that is most relevant such as 'atypical full immortal'. This is essentially the 'not restrict player freedom' category.

• Examples:
  
  • Guyver (B-movie) - atypical full immortality - Restoration is slow (a day or so) and it is more a clone / reconstruction and braintape restoration
    
  • Euki - atypical full immortality - like groot in Guardians of the galaxy but rather than asexual reproduction, the original plant-being slowly grows back slowly over a month but only grows back when sunlight is available.
    
  • Vampires - atypical basic or full immortality - stake through heart kills in most settings inactivates in a rare few, sunlight kills in most settings, other weaknesses, must feed. Atypical-Basic In settings where burning or decapitation are effective. Atypical-Full otherwise.
    
  • Mythological gods - atypical full, near-total, or total immortality - Usually have achilles heals to very rare 'god-killer' types of weapons or magic.