Way of Iron

Monks following the Way of Iron believe strength and willpower are the most powerful forces a mortal can wield. Using the ki within themselves and determination they continue fighting where others would faulter. Iron monks are more than accustomed to the harsh and intense pain that comes with fighting and are capable of enduring and reciprocating any damage they receive.

(Credits for Subclass: DNDBlue on Reddit. Some features were renamed, modified and updated to balance the class out.)

Iron Skin, Steel Bones

At 3rd level, your skin becomes much more durable like iron, preferring to receive hits head on compared to dodging away from them. You can use your Constitution modifier, instead of Dexterity, when determining your AC when using Unarmored Defense. Additionally, you can give yourself a bonus to your initiative rolls equal to that of your Strength modifier.

Constitution + Wisdom

You use your Constitution modifier instead of your Dexterity modifier when determining your AC with Unarmored Defense.

(Read Before Application: If you choose this option, you will need to manually override your AC to make it {10 + CON + WIS}. I formally apologize about the inconvenience and hope it's not too big of a hassle.)

Dexterity + Wisdom

You use your Dexterity modifier instead of your Constitution modifier when determining your AC with Unarmored Defense.

Brace

Also at 3rd level, due to your intense training, you learn how to endure tremendous amounts of pain. As a reaction, you grit your teeth and tense your muscles. Until the start of your next turn, you gain resistance to bludgeoning, slashing and piercing damage. While in this state, you also cannot be knocked prone.

You can use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest. While you have no uses available, you can spend 1 ki points to use this feature again.

Spar

At 6th level, you slam your fists together creating a small sonic pulse, drawing the attention of nearby enemies. As an action, any hostile creature within 30 ft. of you must make a Wisdom saving throw against your Ki Save DC, on a failed save they are goaded for one minute. Goaded creatures have disadvantage on all attack rolls against targets other than yourself. A creature is able to repeat this saving throw at the end of their turn, and if a creature succeeds from their save, they are immune to this feature for 24 hours.

You can use this feature once, and you regain its use when you finish a short or long rest. While you have no uses available, you can spend 3 ki points to use this feature again.

Resolute Strength, Unwavering Constitution

At 11th level, your training sets your strength and bodily will to its limits when its most needed. When you are subjected to a Strength check, you can spend 1 ki points to add your martial arts die to the total. Additionally, when you make a Strength or Constitution saving throw, you can spend 3 ki points to add your martial arts die to the total. For either of these abilities, you must decide to add this before you know the result of the roll.

Unbreakable Force and Spirit

Starting at 17th level, you resist the temptation of death's door, and rely on your own inner strength and willpower to fight through death itself. After succeeding on a death saving throw, you can choose to stand up and act as if you had started your turn conscious. You remain conscious until the end of your turn. While you have 0 hit points during this turn, taking damage causes death saving throw failures as normal, though three death saving throw failures doesn't kill you. At the end of your turn, you fall unconscious if you still have 0 hit points or die if you have three death saving throw failures.
Additionally, you gain advantage on Death Saving throws, which is only applied the first time you fall unconscious. Every subsequent time you fall unconscious after the first without taking a long rest, this additional ability doesn't apply.

Once you use this feature, you can't use it again until you complete a long rest.