Devilman

Whether it be through a deal with a devil, or through possession, you have managed to obtain the power to turn into a demon using your rage, as a devilman you are neither a human or a demon, you are a mix of both. your demon form can come in a variety of things whether it be a humanoid monster or a bull like creature. you can add your own flavor to your abilities depending on what form your demon takes.

Devil form

 once you hit level 3 when you rage you gain the body of a demon, while in your demon form you gain an extra 10ft of walking speed, and you gain +2 strength, and dexterity. this goes up to +4 for either strength or dexterity at level 14. your unarmed attack damage is replaced with a D4 plus your strength or dexterity modifier, this goes up to a d6 at level 10, 

Devil Wings:

 at level 6 when you Rage you sprout wings and gain 25ft flying speed.

devil eyes:

 at level 6 you have a nightvision of 45ft you, you see dark light as if it was dim and dim light as if it was bright

devil ears

 at level 6 you have advantage of perception checks that involve hearing

devil chop

once you hit level 10 while raging you can deliver a mighty punch to an enemy dealing double your extra rage damage on your chart and can knock the enemy back 10 ft.. you can use this once per rage

devil kick

 at level 10 you can deliver a mighty kick to your enemy, this kick deals an extra 1d4 damage and knocks the enemy prone you can use this once per rage

devil endurance

 at level 14 while raging you gain +2 ac.  you are also immune to disease and resistant to poison.

devil beam

at level 14 while raging you can cast scorching ray at level 3, this increases to a level 4 scorching ray at level  16, and a level 5 at level 20

devil cutter

at level 14 once per rage you can destroy your enemy with a mighty blow that deals double your extra barbarian damage plus 1d6, if the attack roll is 4 above the enemys AC any armor there wearing is destroyed, if they are not wearing armor  they're AC is reduced by 3.