Reach 2nd level.
The Ranger gains the Spellcasting feature at 2nd level (Player's Handbook, pg. 91):
By the time you reach 2nd level, you have learned to use the magical essence of nature to cast spells, much as a druid does.
The ranger is what is commonly called a "half-caster", the highest level spells they can ever cast is 5th, which they can ...
Undead don't have a dedicated language
In general, they speak languages they knew in life. Here's a couple of examples:
Languages understands the languages it knew in life but can't speak
Languages the languages it knew in life
Languages Understands all languages it knew in life but can't speak
There are plane-specific undead like ...
Using the optional rule from Xanathar's Guide to Everything, this works
This optional rule states:
Most effects in the game happen in succession, following an order set by the rules or the DM. In rare cases, effects can happen at the same time, especially at the start or end of a creature’s turn. If two or more things happen at the same time on a character ...
This feels like a lateral change
The ability for the ranger to sense the presence of a large variety of creatures is a pretty useful tool, so replacing that with something that just shifts their favored terrain (and doesn't provide the higher level language change) doesn't do a whole lot in term of every-day capability or really improve much on the existing.
I will say no, it is not balanced.
Essentially, your Ranger will have permanent "favored" benefit in whichever terrain he finds himself and against whichever primary opponent he is currently fighting, as those can be adjusted almost at will.
Perhaps if it could only be changed after a long rest; though even with that, it seems like it should ...
No, it doesn't
The rules for opportunity attacks state the following (emphasis mine):
You don’t provoke an opportunity attack when you teleport or when someone or something moves you without using your movement, action, or reaction.
Gathered Swarm clearly states that the swarm moves you. Furthermore, this movement does not use your action (as it is a rider ...
Golems are not humanoid
Page 6 of the Monster Manual introduces the concept of creature type:
A monster's type speaks to its fundamental nature. Certain spells, magic items, class features, and other effects in the game interact in special ways with creatures of a particular type. For example, an arrow of dragon slaying deals extra damage not only to ...
It's all about Creature Tags
"Humanoid" is a creature type, like "Undead" or "Fey". So a creature only counts as humanoid (mechanically speaking) if its stat block declares it as a humanoid creature. Don't look into fluff texts of creature descriptions. All that counts are the creature's type/tags, when it comes to whether that ...
Golems are constructs, not humanoids.
The Favored Enemy feature refers to the creature’s type:
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.
In addition to being Human/Half-Elf/Half-Orc, you could be a Kobold! The level 1 Kobold feat Snare Setter gives you Snare Crafting for free... and if you like snare crafting, then there are some excellent reasons to be a Kobold.
A couple of notes: This subclass has 2 features that involve being attacked, so I will assume this class is intended to be for a melee ranger as opposed to a ranged ranger, in order to take advantage of these abilities. It is perfectly fine for a subclass to specialize with one weapon type over another, and I will be reviewing based on that.
This is technically ambiguous
There is no RAW way to hide in a camp site without magic/sleeping location. Stealth is explicitly used for movement
Usually none. Normally, you make a Stealth check as part of movement, so it doesn’t take a separate action. However, using Stealth immediately after a ranged attack (see Sniping, above) is a move action.