The following is an alternative / full replacement of the Hunter subclass for use in my campaigns.
Hunters are relentless pursuers of all manner of creatures, across all manner of terrain. Once a Hunter marks a target, it doesn't much matter whether their prey runs and hides or stands and fights. Hunters are adaptable, able to switch up their tactics, exploit any weaknesses, and evade or mitigate counterattacks as necessary to bring down their current quarry.
Some Hunters develop a keen awareness of their chosen prey, some master how to track, and others excel in the pursuit. You gain one of the following feature options of your choice.
*Know the Course. Your Speed increases by 10 feet and difficult terrain does not slow your movement. In addition, you do not suffer Disadvantage on Wisdom or Dexterity checks due to moving at a Fast pace.
*Know the Mark. You can cast Hunter's Mark without need of spell components. In addition, while a creature is marked by your Hunter's Mark, you know all Immunities, Resistances, and Vulnerabilities the creature has, if any. Furthermore, while you are on the same plane of existence as the creature, you have a sense of their relative health (Healthy, Bloodied, Unconscious, Dead), stamina (how many levels of Exhaustion they currently have), their relative distance from you (near, mid, far), and if they are moving.
*Know the Quarry. You gain proficiency with Survival. If you already are proficient in Survival, you gain Expertise in Survival instead. In addition, you can Search as a Bonus Action to make a Wisdom (Survival) check to track or find a trail, and you roll with Advantage when you do so.
You gain one of the following feature options of your choice.
*Collateral Mark. Once per turn when you make an attack with a weapon against the target of your Hunter's Mark, you can make another attack with the same weapon against a different enemy creature that is within the weapon's range.
*Persistent Attrition. Once per turn when you make an attack with a weapon targeting a creature that has less than their maximum Hit Points, you may add your Wisdom modifier as a bonus to both hit and damage.
When you roll Initiative, you can replace your currently chosen Tactical Techniques option with the other option. You can use this feature once initially and twice after you reach ranger level 11, regaining all uses when you finish a Long Rest.
You gain one of the following feature options of your choice. Additionally, when you use your Whatever Works feature you can replace your currently chosen option from this feature with the other option.
*Adaptive Defense. When a creature hits you with an attack roll, that creature has Disadvantage on all other attack rolls against you until the start of your next turn.
*Warding Mark. Once per turn when you are subjected to an effect by the target of your Hunter's Mark that allows you to make a saving throw, you can choose to gain Advantage on that saving throw.
You gain one of the following feature options of your choice. Additionally, when you use your Whatever Works feature you can replace your currently chosen option from this feature with the other option.
*Sniper's Mark. If you have the Hide action's Invisible condition, making an attack against the target of your Hunter's Mark doesn't end that condition on you if you end your turn behind Three-Quarters Cover or Total Cover.
*Target of Opportunity. When a creature that you can see starts or ends their turn within range of a weapon you are holding, you can take a Reaction to make a weapon attack against that creature with that weapon.
You gain one of the following feature options of your choice. Additionally, when you use your Whatever Works feature you can replace your currently chosen option from this feature with the other option.
*Death Mark. While this option is selected, you may change the damage type of your Hunter's Mark extra damage from Force to a damage type that you know the marked target is Vulnerable to, and your Hunter's Mark no longer requires Concentration. In addition, when your Hunter's Mark would end while the current marked target is alive and on the same plane of existence, you may expend a spell slot to extend the Duration of the spell by the appropriate amount for the expended slot's spell level.
*Evasion. When you are subjected to an effect that allows you to make a Dexterity saving throw to take only half damage, you instead take no damage if you succeed on the saving throw, and only half damage if you fail.