Ingenious Tracker

Unlike other Rangers, you rely upon intellect over instinct and magical ability. Every creature has a weakness or vulnerability, and your research lets you find it. Extensive study and observation allows you to teach your allies where best to strike. Your Intelligence further lets you manipulate creatures’ physiology to stun or cause pervasive damage.

Anatomical Advantage

Starting at 3rd level, you begin to rely on what you know, not what you feel. Intelligence is now your spellcasting ability for your ranger spells. You use your Intelligence whenever a spell refers to your spellcasting ability. In addition, you use your Intelligence modifier when setting the saving throw DC for a ranger spell you cast and when making an attack roll with one.

Spell save DC = 8 + your proficiency bonus + your Intelligence modifier

Spell attack modifier = your proficiency bonus + your Intelligence modifier

The Foe Slayer feature at 20th level uses your Intelligence modifer instead of the Wisdom modifier.

Study Buddies

Every Ranger knows, “the strength of the pack is the wolf, and the strength of the wolf is the pack”. From level 3 onward, whenever your allies are engaged with your favored enemies you can direct them where and how to most effectively strike. As a bonus action, you can grant a 1d6 Knowledge Die for 10 minutes to a number of creatures (equal to your Intelligence modifier, minimum of 1) other than yourself that are within 60 feet. A Knowledge Die can be applied to weapon damage or weapon attack rolls against your favored enemies. A creature may apply only one Knowledge Die per a given attack.

You may use this feature twice per short rest. 

At level 15, you gain an additional use of Study Buddies per short rest.

Knowledge is Power

At level 7, you begin to pick up on creature behavior patterns and characteristics much quicker than others gaining. You may choose an additional type of  favored enemy: aberrations, beasts, celestials, constructs, dragons, elementals, fey, fiends, giants, monstrosities, oozes, plants, or undead. Alternatively, you can select two races of humanoid (such as gnolls and orcs) as favored enemies.

You also gain the Strike to Stun feature. You’ve learned how to disrupt the nervous systems for a number of foes. Your weapon attacks score a critical hit on a roll of 19 or 20. When you roll a critical hit for a weapon attack, the target is stunned until the end of your next turn. 

The target can only suffers from one Strike to Stun effect at a time. Multiple instances of this feature do not stack. This feature does not affect undead, constructs, or other creatures without functioning neural networks (up to DM discretion.) 

Aberrations

Aberrations are utterly alien beings. Many of them have innate magical abilities drawn from the creature's alien mind rather than the mystical forces of the world. The quintessential aberrations are aboleths, and slaadi.

Beasts

Beasts are nonhumanoid creatures that are a natural part of the fantasy ecology. Some of them have magical powers, but most are unintelligent and lack any society or language. Beasts include all varieties of ordinary animals, dinosaurs, and giant versions of animals.

Celestials

Celestials are creatures native to the Upper Planes. Many of them are the servants of deities, employed as messengers or agents in the mortal realm and throughout the planes. Celestials are good by nature, so the exceptional celestial who strays from a good alignment is a horrifying rarity. Celestials include angels, couatls, and pegasi.

Constructs

Constructs are made, not born. Some are programmed by their creators to follow a simple set of instructions, while others are imbued with sentience and capable of independent thought. Golems are the iconic constructs. Many creatures native to the outer plane of Mechanus, such as modrons, are constructs shaped from the raw material of the plane by the will of more powerful creatures.

Dragons

Dragons are large reptilian creatures of ancient origin and tremendous power. True dragons, including the good metallic dragons and the evil chromatic dragons, are highly intelligent and have innate magic. Also in this category are creatures distantly related to true dragons, but less powerful, less intelligent, and less magical, such as wyverns and pseudodragons.

Elementals

Elementals are creatures native to the elemental planes. Some creatures of this type are little more than animate masses of their respective elements, including the creatures simply called elementals. Others have biological forms infused with elemental energy. The races of genies, including djinn and efreet, form the most important civilizations on the elemental planes. Other elemental creatures include azers, invisible stalkers, and water weirds.

Fey

Fey are magical creatures closely tied to the forces of nature. They dwell in twilight groves and misty forests. In some worlds, they are closely tied to the Feywild, also called the Plane of Faerie. Some are also found in the Outer Planes, particularly the planes of Arborea and the Beastlands. Fey include dryads, pixies, and satyrs.

Fiends

Giants

Giants tower over humans and their kind. They are humanlike in shape, though some have multiple heads (ettins) or deformities (fomorians). The six varieties of true giant are hill giants, stone giants, frost giants, fire giants, cloud giants, and storm giants. Besides these, creatures such as ogres and trolls are giants.

Humanoids

Humanoids are the main peoples of a fantasy gaming world, both civilized and savage, including humans and a tremendous variety of other species. They have language and culture, few if any innate magical abilities (though most humanoids can learn spellcasting), and a bipedal form. The most common humanoid races are the ones most suitable as player characters: humans, dwarves, elves, and halflings. Almost as numerous but far more savage and brutal, and almost uniformly evil, are the races of goblinoids (goblins, hobgoblins, and bugbears), orcs, gnolls, lizardfolk, and kobolds.

Monstrosities

Monstrosities are monsters in the strictest sense -- frightening creatures that are not ordinary, not truly natural, and almost never benign. Some are the results of magical experimentation gone awry (such as owlbears), and others are the product of terrible curses (including minotaurs). They defy categorization, and in some sense serve as a catch-all category for creatures that don't fit into any other type.

Oozes

Oozes are gelatinous creatures that rarely have a fixed shape. They are mostly subterranean, dwelling in caves and dungeons and feeding on refuse, carrion, or creatures unlucky enough to get in their way. Black puddings and gelatinous cubes are among the most recognizable oozes.

Plants

Plants in this context are vegetable creatures, not ordinary flora. Most of them are ambulatory, and some are carnivorous. The quintessential plants are the shambling mound and the treant. Fungal creatures such as the gas spore and the myconid also fall into this category.

Undead

Undead are once-living creatures brought to a horrifying state of undeath through the practice of necromantic magic or some unholy curse. Undead include walking corpses, such as vampires and zombies, as well as bodiless spirits, such as ghosts and specters.

If It Bleeds, I Can Kill It

At level 11, your experience in battle allows you to deal extra damage to any favored enemy that can bleed. Once per turn, when you make a successful weapon strike against a target, you can cause bleeding damage to it. The target bleeds 1d4 damage at the end of each of their turns. This damage increases by 1d4 for ever 10 feet of distance the target moved since the end of their last turn. If the target is healed, the bleeding staunched with a DC 15 Medicine check, or the target passes a Constitution saving throw, the effect ends. 

You may choose to take an action to staunch the bleeding of a willing or unconscious target by making a DC 15 Medicine check with advantage. 

This feature does not effect undead, constructs, or other creatures without blood (up to DM discretion.) This damage does not increase for distances teleported. The target can only be affected once by the effects of this feature at a time. 

Prodigious Biologist

By level 15, your widespread study of creatures has allowed you to quickly learn about any target. All creatures with an active Hunter’s Mark are also treated as favored enemies for the duration of the spell. You have advantage on Wisdom (Survival) checks to track your favored enemies, as well as on Intelligence checks to recall information about them.