Slayer (5e Subclass)
From D&D Wiki
At the 3rd level, you gain proficiency in one of the following skills: Arcana, Religion, or Nature. Your proficiency bonus is doubled for this skill.
At level 3, you gain one of the following traits of your choice:
- Battle Fervor. Whenever you use your Action Surge, you gain advantage on attack rolls until the end of your turn.
- Fanatic Resolve. Whenever you gain HP from your Second Wind ability, you gain Temporary HP equal to your Constitution Modifier + your Fighter Level.
- Danger Sense. You gain an uncanny sense of when things nearby aren’t as they should be, giving you an edge when you dodge away from danger. You have advantage on Dexterity saving throws against effects that you can see, such as traps and spells. To gain this benefit, you can’t be blinded, deafened, or incapacitated.
Beginning at 7th level, you have significant experience studying, tracking, hunting, and even talking to a certain type of enemy.
Choose a 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 have advantage on Wisdom (Survival) checks to track your favored enemies, as well as on Intelligence checks to recall information about them.
When you gain this feature, you also learn one language of your choice that is spoken by your favored enemies, if they speak one at all.
At level 10, you gain one of the following traits of your choice:
- Spellbreaker. Whenever a creature within 5 feet of you casts a spell, you may use your reaction to force the creature to make a Constitution save (DC = 8 + Proficiency Bonus + your Strength/Dexterity Modifier). On a failure, the caster suffers disadvantage on attack rolls for that spell.
- Refreshing Strike. When you use your Second Wind feature, you may make a weapon attack.
- Resilience. When you use your Indomitable feature, you have advantage on the next saving throw that you make within the next minute.
By 15th level, you have acquired greater mental strength. You gain proficiency in Wisdom saving throws.
At level 18, you gain one of the following traits of your choice:
- Adrenaline Surge. When you use your Action Surge, you can take one of the following actions in addition to the extra action: Dash, Disengage, Dash, or Hide.
- Resolute Defiance. When you use your Second Wind, you can end one effect on yourself if it can be ended with a saving throw.
- Spell Turning. When you use your Indomitable feature on a saving throw against a spell, you may roll an additional die and use either roll.
The vast majority of credit goes to Zetesofos, on reddit, although I made a few alterations.