Circle of the Archfiend

Druids of the circle of the archfiend take on the form of a devil from the nine hells or a demon from the abyss, to protect nature and the plane they live in from other otherwordly threats. They are able to gain this form by trapping a devil or a demon when that creature is at their most vulnerable, or when they have slain it.

Fiendish Legacy

Starting at 2nd level, you gain proficiency with either Charisma (Intimidation) or Charisma (Deception) skills. If you already have proficiency with your chosen skill, you gain expertise instead. You also gain proficiency with both simple and martial weapons and you learn to speak and write Infernal or Abyssal.

Abyssal

You gain knowledge of the Abyssal language.

Charisma (Deception)

You gain proficiency in the Charisma (Deception) skill. If you already have proficiency, you instead get expertise.

Charisma (Intimidation)

You gain proficiency in the Charisma (Intimidation) skill. If you already have proficiency, you instead get expertise.

Infernal

You gain knowledge of the Infernal language.

Circle of the Archfiend Spells

You gain the following spells at the following spell levels, added to your spell list. These count as druid spells for you.
2nd Flame Blade
3rd Summon Lesser Demon
4th Summon Greater Demon
5th Telepathic Bond
6th Summon Fiend

Form of the Fiend

Starting at 2nd level, you can expend a use of your Wildshape feature, to take on the form of a Devil or a Demon. This transformation lasts for 10 minutes, and while transformed your AC become 13 + your Dexterity modifier + your Wisdom modifier. When you transform you gain one of the following abilities:

Fiendish Resistance: You gain resistance to either Fire damage (Devil form) or Cold damage (Demon form). You also gain 1d6 temporary hit points when you transform

Fiendish Assault: Your unarmed strikes deal either Fire damage (Devil form) or Cold damage (Demon form). Your unarmed strikes also deal 1d8 + your Wisdom modifier damage. You can also use your Wisdom modifier for any attacks you make with a Simple or Martial weapon you're proficient with.

Fiendish Blast: As a bonus action on your turns, you can make a magical ranged attack to a target within 60ft. of you. On a hit, that target takes 1d8 + your Wisdom modifier Fire damage (Devil form) or Cold damage (Demon form)

Fiendish Assault (Cold)

Fiendish Assault: Your unarmed strikes deal either Fire damage (Devil form) or Cold damage (Demon form). Your unarmed strikes also deal 1d8 + your Wisdom modifier damage. You can also use your Wisdom modifier for any attacks you make with a Simple or Martial weapon you're proficient with.

Fiendish Assault (Fire)

Fiendish Assault: Your unarmed strikes deal either Fire damage (Devil form) or Cold damage (Demon form). Your unarmed strikes also deal 1d8 + your Wisdom modifier damage. You can also use your Wisdom modifier for any attacks you make with a Simple or Martial weapon you're proficient with.

Fiendish Blast (Cold)

Fiendish Blast: As a bonus action on your turns, you can make a magical ranged attack to a target within 60ft. of you. On a hit, that target takes 1d8 + your Wisdom modifier Fire damage (Devil form) or Cold damage (Demon form)

Fiendish Blast (Fire)

Fiendish Blast: As a bonus action on your turns, you can make a magical ranged attack to a target within 60ft. of you. On a hit, that target takes 1d8 + your Wisdom modifier Fire damage (Devil form) or Cold damage (Demon form)

Fiendish Resistance (Cold)

Fiendish Resistance: You gain resistance to either Fire damage (Devil form) or Cold damage (Demon form). You also gain 1d6 temporary hit points when you transform

Fiendish Resistance (Fire)

Fiendish Resistance: You gain resistance to either Fire damage (Devil form) or Cold damage (Demon form). You also gain 1d6 temporary hit points when you transform

Normal

Select this when you are not in your transformed state.

???

Honestly this is just here because DNDBeyond was complaining it needed a 3rd level feature for druid(?)

Fiend Improvements

Starting at 6th level, you have improved and strengthened your fiendish powers. While you have your Form of The Fiend active, the features you gain from Form of The Fiend gain the following benefits:

Fiendish Resistance: Instead of gaininng resistance to Fire or Cold damage, you can gain resistance to Force Damage, the temporary hit points you gain increase to 2d6 Temporary Hit Points.

Fiendish Assault: Instead of Fire or Cold damage, your Unarmed Strikes can deal Force Damage. Also, as a bonus action, you can make a second Unarmed Strike or Weapon attack with a Weapon you're proficient with.

Fiendish Blast: Instead of Fire or Cold damage, the blast you fire from your Fiendish Blast benefit can deal Force Damage. You can also fire a blast as part of your main action. This blast deals 1d10 + your Wisdom modifier Fire damage (Devil form) or Cold damage (Demon form), or Force damage.

Fiend Flight

At 10th level, when you take on your Form of the Fiend, you can gain flight speed equal to your Movement Speed until the end of your transformation. You can only use this feature an equal amount to your Proficiency Bonus. You regain all expended uses on a long rest.

Druidic Archfiend

Finally at 14th level, you have reached your Zenith as a member of the Circle of the Archfiend. You also gain all of the 3 benefits that feature grants you, instead of the one. Your three Form of the Fiend benefits also gain these additional effects added to them:

Fiendish Resistance: You gain a +2 bonus to your AC, and you can add your Wisdom modifier to any Saving Throws you make.

Fiendish Assault: You can attack twice, instead of once, whenever you take the Attack action on your turn.

Fiendish Blast: On your turn, you can forgo your Bonus Action and any Action you would have taken, to fire a powerful fiendish blast. You fire the blast to a point of your choice, and any creature of your choice there (an amount of creatures equal to your Wisdom modifier) must make a Dexterity Saving Throw with DC equal to your Spellcasting Save DC. On a failed save, they take 5d8 Fire damage (Devil form), Cold damage (Demon form) or Force damage, or half as much on a successful save.

Additionally, your maximum hp is increased by an amount equal to your druid level, your wild shapes also gain this benefit.