Hello, this is my first homebrew and I'd like some opinions on it particularly regarding balance. I'm a huge fan of the Styx series and unfortunately was unable to find a truly good archetype to fit the character of Styx so I decided to make my own and this is what I came up with. I decided to start with the Alchemist class as the base as I wanted to play up Amber and allow for a reasonable excuse for the ability of Amber Twin. I also decided against giving this character flat invisibility and instead gave it access to large Stealth bonuses as this was made with the Hobgoblin race in mind (and their +4 to Stealth checks).

(I would post the base Alchemist for reference but I'm unable to post links due to my post count)
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The Amber Alchemist

Stealth
The Amber Alchemist replaces the Class Skill Knowledge (Arcana) with the Stealth skill

Sneak Attack
At 1st level an Amber Alchemist gains the Sneak Attack ability as a Rogue of the same level.
This replaces the Alchemist’s Bomb ability

Amber Mutagens
Amber Alchemists focus on Mutagens to the near exclusion of all other alchemical research and cannot create Extracts.
At 1st level this mastery gives the Amber Alchemist a +1 bonus to Attack rolls while under the effects of a Mutagen that he has created. At 5th level and every 4 levels thereafter this bonus increases by +1.
This ability changes Alchemy and Mutagens

Theft
You may choose the Combat Swipe rogue talent in place of a Discovery

Amber Twin
At 5th level you may use Vomit Twin as a Spell-Like ability once per day. At 8th level and every 3 levels thereafter you may use Vomit Twin an additional time per day up to a maximum of 5 times per day at 20th level.
This ability replaces Brew Potion and Throw Anything