Mark of the Monstrosity

You've tamed a monstrosity and the pair of you fight as one.

Ranger’s Monstrous Companion

At 3rd level, you gain a Monstrosity companion that accompanies you on your adventures and is trained to fight alongside you. Choose a Monstrosity that is no larger than Large and that has a challenge rating of 2 or lower. Its hit point maximum equals the hit point number in its stat block or four times your ranger level, whichever is higher. Like any creature, it can spend Hit Dice during a short rest to regain hit points.

The Monstrosity is friendly to you and your companions and obeys your commands. In combat, the Monstrosity shares your initiative count, but it takes its turn immediately after yours. On your turn, you can verbally command the beast where to move (no action required by you). The only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take one of the actions in its stat block or to take the Dash, Disengage, Help, or Hide action.

If you are incapacitated or absent, the beast acts on its own, focusing on protecting you and itself. The Monstrosity never requires your command to use its reaction, such as when making an opportunity attack.

While traveling through your favored terrain with only the beast, you can move stealthily at a normal pace.

If the Monstrosity goes to 0 hp then it has 3 death saves that work like a player.
If the Monster dies you can perform a ritual spell which summons a new body for your monster. You must knock the new creature unconscious for the spirit of your previous creature to capture its body. (be warned the summoning ritual may summon more monsters than just the creature you want to summon.)

Exceptional Connection

While your Companion is within 100 feet of you, you can communicate with it telepathically. Additionally, as an action, you can see through your Companion’s eyes and hear what it hears until the start of your next turn, gaining the benefits of any special senses that the familiar has.

In addition, the Companion's attacks now count as magical for the purpose of overcoming resistance and immunity to nonmagical attacks and damage.

Off the Leash

Starting at 11th level, when you can command your companion to "Release" its restraints.

While released your creatures attacks Recklessly, (it gets advantage on melee weapon attack rolls using Strength during this turn, but attack rolls against it have advantage until its next turn.)
It gains movement bonus equal to (5ft)x(wisdom modifier).
It gains 2 reactions for attacks of opportunity.
it have advantage on Strength checks and Strength saving throws.
it have resistance to bludgeoning, piercing, and slashing damage.
When its deals damage it does additional damage equal to your (wisdom modifier + your monsters strength modifier).

If the Monstrosity doesn't take damage or deal damage the release ends.

You can Use this feature a number of time equal to your wisdom modifier.

Holding on to Life

Beginning at 15th level, when you are at 0 hp if your companion is within 20ft of you. It can take necrotic damage, for every 2 points of damage it takes, you regain 1 hp. Your companion cant bring itself to 0 hp, as it is the tether keeping your spirit on the current plane. you can use this ability once per long rest.