The Boneless

This subclass is inspired by the interpretation of Ivar the Boneless from the television series "Vikings." The idea behind it is that the player character suffers from some sort of disease, paralysis, or condition that has caused the loss of use of their legs. The character will have likely lived in a society centered around battle or lived through some other hardship that forced them to stand up and fight, or rather, get down and fight. With limited movement, the drawbacks will be major, but the benefits will also be great if the class is played well. I hope it will add a nice flavor to your game and mine. 

Crawling Prowess

You have had to learn to fight while crawling on your hands, giving you strong reactional movement on the ground. At 3rd level melee attacks against you do not take advantage because you are prone. Ranged attacks, however, will still have disadvantage to hit you. This feature is negated if you are wearing heavy armor or if you are over encumbered.

Crippled Movement

Your condition is a burden to you and has hindered your movement. Upon taking this subclass, your movement speed is halved, and all dexterity checks and saving throws have disadvantage while you are not riding a mount. Additionally, you are unable to effectively use two handed martial weapons. All attacks with two handed martial weapons will be at disadvantage.

Equal Terms

At 7th level, you learn to fight on your own terms, taking a home field advantage. You can rip your opponents to the ground to make them fight on your terms. Grappling checks in which you are pulling a target prone now have advantage and deal bludgeoning damage that will scale with your level.

War Cry

Most underestimate your capabilities, but seeing you fight, they assume you to be something... unnatural. At 10th level, once you have either incapacitated or hit an enemy with a critical strike in an encounter, you may use an action to let out your "War Cry," forcing all enemies that can hear you to make a WIS saving throw (DC=8+STR+PROF). On a failed save, the target will become frightened of you for 1 minute. Additionally, your first successful attack on each target will be critical hits. On a successful save, this has no effect. This ability can be used once per short rest.

You gain additional uses of this feature at levels 14 and 18.

Pig Slaughter

Your fighting from the ground grows more brutal. At 15th level, when you attack creatures that are prone with a melee weapon or unarmed attack, a natural dice roll of 17 or higher results in a critical hit. Additionally, when you gain a critical hit on a prone target, you may reroll all damage dice that result in a 1.

Forced Empathy

At 18th level, you have a chance to make someone suffer as you have. On a successful critical attack, you can ask your DM to roll a d100. With a result of 5 or below, the target loses the ability to use their legs.