Otherworldly Companion

Your Animal Companion, or summoned Familiar or Mount is more than a simple beast. 

Requisite: Animal Companion Ranger ability, ability to cast Find Familiar or Find mount.

When you take this feat you choose if your companion is either a celestial, construct, fey, fiend or undead creature. This choice determines the abilities it gains and cannot be changed once chosen.    

• Celestial:
  • Immunity to radiant damage
  • Resistance to cold and lightning
  • Natural attacks are considered magical and good
  • Understand common and celestial but only gains the ability to speak celestial
  • Can be targeted by effects that specifically affect either celestials or beasts
• Construct:
  • Does not require food, water, air or sleep
  • Immune to poison, disease and the poisoned condition 
  • Cannot be healed by magic intended for living creatures
  • Understands common and machine speak but can only speak machine speak
  • Can be targeted by effects that specifically affect either constructs or beasts
• Fey:
  
  • Resistance to bludgeoning, piercing and slashing damage from non-magical weapons that are not cold iron.
  • Has advantage on saving throws against enchantment effects
  • Can speak with any beast as if under the effect of "Speak with Animals"
  • Understands common and sylvan but can only speak sylvan
  • Can be targeted by effects that specifically affect either fey or beasts
• Fiend
  • Immunity to fire damage
  • Resistance to acid and necrotic damage
  • Natural attacks are considered magic and evil
  • Understand common and fiendish but only gains the ability to speak fiendish
  • Can be targeted by effects that specifically affect either fiends or beasts
• Undead
  • Does not require food, water, air or sleep
  • Immune to necrotic and poison damage as well as disease and the poisoned condition 
  • Cannot be healed by magic intended for living creatures
  • Understands common but does not gain the ability to speak
  • Can be targeted by effects that specifically affect either undead or beasts

It also gains the following bonuses regardless of what type of creature you chose

• Darkvision 60
• Intelligence ability equal to 6 + your proficiency bonus unless it has an intelligence higher than this already
• Hit points equal to 4 x (your levels in whatever class grants you the companion), unless it has more hit points than this already