This homebrew subclass is something I came up with to compensate for the fact that my group has only three members, and I as a monk am the only one remotely capable of tanking.
I call it the Way of the Iron Fist:
Way of the Iron Fist
You are a monk who has forged yourself into a weapon after years of brutal training and hardship to atone for a past evil and fight as a defender of the common people.
At third level when you assume this tradition, your fists and feet become as hard as iron from years of brutal training in martial arts. This grants you the ability to deal 3 extra damage on unarmed strikes. Your fists also have the ability to strike the ki of the creature that you are striking, allowing you to siphon their ki and regain up to 3 HP per melee attack if you are striking an enemy while injured.
At third level, due to the iron strength of your limbs, you are capable of blocking melee weapons with your hands. If a melee attack hits you, you can choose as a reaction to make a Dexterity saving throw against your ki save DC; if you succeed on the saving throw, you can, as a last ditch defense, catch the melee weapon with your hands to deflect the blow.
At sixth level, you can have an extra strike added to Flurry of Blows.
Upon reaching 11th level, your will has become as strong as iron from brutal mental conditioning and transcending your fears to resist those who attempt to control your mind. You cannot be charmed, frightened, or put to sleep. You also gain resistance to psychic damage, and creatures cannot see your thoughts or intentions due to your strength of mind.
After years of self-imposed hardship to toughen your body, your entire body has become as strong as iron. You no longer feel pain and cannot be incapacitated by physical blows, and gain resistance to bludgeoning, slashing, and piercing damage.
I really love this subclass idea as it fits perfectly with my character's backstory, but I am afraid it would make them way too overpowered and unbalance the game.
Is there any way maybe I should change it to make it less overpowered if it is too strong?