Vivisectionist

A vivisectionist studies bodies to better understand their function. Unlike a chirurgeon, a vivisectionist's goals are not related to healing, but rather to experimentation and knowledge that most people would consider evil.

Medical Discovery

Starting at 3rd level, you loose Thieves’ Cant and Cunning Action rogue class features, but instead you give some of them to your Greatest Experiment. It gains Uncanny Dodge and Evasion rogue class features at the same level as you.

You also gain a proficiency with Alchemy tools. When any spell is effect applied to you, while within 30 ft. the great experiment can choose to also be affected by it.

The Greatest Experiment

By 3rd level, your vile tests has borne you a faithful companion, the greatests experiment. It is friendly to you and your companions, and it obeys your commands. See this creature's game statistics in the greatests experiment stat block. You determine the creature's appearance and whether it has two legs or four; your choice has no effect on its game statistics.

In combat, the greatests experiment shares your initiative count. It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take one of the actions in its stat block or the Dash, Disengage, Help, Hide, or Search action.

Instead of a short rest, you can spend an hour mending the greatests experiment, if you do so, it will regains all of its hit points.

At the end of a long rest, you can create a new greatests experiment if you have your alchemist's tools with you. If you already have a greatests experiment from this feature, the first one immediately perishes.

Contaminated monstrosity

Starting at 9th level, you inject a feral mutagen into the greatest expriment for 1 minute, it increases its movement speed by 20,  can add 3 to their strength checks and their melee weapon damage and regenerates 10 hit points per turn. It must also subtract 5 from their INT and WIS checks.

You can only use this feature once per long rest.

"Friendly" experiment

By 13th level, you can give any of your "friends" a resistance to a damage type as an action for up to 10 minutes. You choose duration of this effect when it is applied. For every minute of resistance target's maximum hit points are reduced by 2d6. Target regains its hit point maximum after a short rest.

Perfect body

Starting at 17th level you’ve built a resistance to chemicals that an average person cannot take. You use your newfound resistance to enhance your body. You can only administer the volatile mix to yourself once a day. You mutate into a huge creature and become resistant to bludgeoning, piercing, slashing, acid, fire, cold, force, and lightning damage. Your unarmed strikes have +8 to hit and do 6d6 bludgeoning damage + your dexterity modifier, it can still apply sneak attacks. Lasts 10 minutes.

Permanently Immune to Poison and the Poisoned status effect.