Necrosis

If a creature has been touched by a powerful source of necromancy magic, there is the possibility of having a limb shrivel up. The creature must make a Constitution saving throw, where the DC is 10 or half as much necrotic damage you take, whichever is higher. This is similar to the Withered condition but systemic.
A creature with necrosis has disadvantage on Strength, Dexterity, and Constitution saving throws and ability checks. Each day the creature is afflicted with necrosis, make a DC 10 CON saving throw or the creature's MAX HP is reduced by 1d6.
Treating necrosis requires a DC 15 Intelligence (Arcana) or Wisdom (Medicine) check. On a success, the necrotic energy does not travel further into the body and stops the daily checks. Only one Intelligence (Arcana) or Wisdom (Medicine) check can be attempted per day.
This affliction can be cured with the regenerate spell or similar magic.
A greater restoration or similar powerful spell will heal a withered limb.