Hi, I'm also working on a tweak to the Ranger class (given that I love it thematically but as is needs to be CharOp-ed to compete with the other classes in combat). Here's what I have for level 20 seeing as Foe Slayer is so... Meh
Peerless Tracker: You can never gain disadvantage on Wisdom (Perception) and Wisdom (Survival) checks, and creatures cannot evade your tracking by any means, magical or otherwise. Additionally, enemies under your Hunter’s Mark always count as Favored Enemies (if it already is a Favored Enemy, increase damage to 1d10 [//I made Hunter's Mark a Class Ability with added damage and tracking bounses against Favored Enemies]); you always know which direction they are in regardless of distance, and if they are in a different plane you know which one.
Peerless Tracker: You can never gain disadvantage on Wisdom (Perception) and Wisdom (Survival) checks, and creatures cannot evade your tracking by any means, magical or otherwise. Additionally, enemies under your Hunter’s Mark always count as Favored Enemies (if it already is a Favored Enemy, increase damage to 1d10 [//I made Hunter's Mark a Class Ability with added damage and tracking bounses against Favored Enemies]); you always know which direction they are in regardless of distance, and if they are in a different plane you know which one.