Innate Spellcasting. The crimson fiend's spellcasting ability is Charisma (spell save DC 12, +4 to hit with spell attacks). It can innately cast the following spells, requiring no material components: At will: fire bolt, elemental blade 1/day each: burning hands, scorching ray
Fiery Form. As a bonus action, the crimson fiend can turn into a form of pure elemental fire until the start of its next turn. While in this form, it is immune to all damage except cold damage but can't attack any creature. It gains a flying speed of 20 ft. and gains immunity against prone, restrained, and paralyzed conditions. If it ends its turn in a creature's space, it takes 6 (1d10) force damage while the creature takes 2 (1d4) fire damage. While in this form, it can squeeze through openings as narrow as 1 inch, such as a keyhole or similar.
Actions
Flame Fist. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 2) bludgeoning damage plus 4 (1d6) fire damage.
Eruption. Il Rosso targets a point within 60 ft. of it. Flame erupts from the point and creatures within 10 ft. of that point must succeed on a DC 12 Dexterity saving throw or start burning for 1 minute. A burning creature takes 4 (1d6) fire damage at the start of each of its turns for the duration. Only water from a spell can put out the flames. On a successful save, a creature takes only 2 (1d4) fire damage.
Breathing Fire
They are what remain of sacrificed souls who were thrown into the fires of endless torment and who clawed their way out through sheer hatred. They look for revenge and retribution, and if they cannot find it they take out their malic on whatever may fall in their path. Appearing as a skeleton or zombie with cracks in their body filled with red hot flame or white fire traces, they are a sight not easily forgotten. They can control fire, and are immune to it as most fiends are.
Servants of Evil
They are usually conjured by cultists as a means to terrorize their enemies, inflict fear upon them, or as a punishment for a fellow cultist, an adversary, or a rival to condemn their soul for eternity. It is also possible for humanoids filled with hatred and fury to rise as Il Rosso after they suffer a deadly injury during a fire.