Physical Durability. The zinfernit has an incredibly strong armor, gaining 10 damage reduction against all physical attacks.

Self Weakened. One of their only weaknesses is their own weapon, taking 10 bonus damage from an "Infernal Greatsword".

Fireproof. The zinfernit are immune to fire damage.

Freezing Weakness. Having an inerrant weakness to cold, they get significantly weaker in winter and/or generally colder areas (Temperatures colder than 0 degree celsius): They lose 10 in all positive damage reductions, -6 on a hit roll, -6 on a damage roll and -6 on AC.

Magic spells that imitate cold weather also affect the zinfernit in the same way until after their next turn.

Fist. Melee Weapon Attack: +12 to hit, reach 5 ft., one creature. Hit: 9 (1d8 + 5) bludgeoning damage.

Infernal Greatsword. Melee Weapon Attack: +12 to hit, reach 10 ft., one creature. Hit: 12 (2d6 + 5) slashing damage plus 10 (3d6) fire damage and the target must succeed a DC 12 Constitution saving throw or take 7 (3d6) fire damage at each of their next turn until they die. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.