You spent a significant amount of time in captivity—or at least confinement—where you were changed in some way. No longer, though; now you are free in the world and able to choose your own path.
Were you imprisoned and experimented on against your will, or was it voluntary? Did you experiment on yourself? How do you feel about the results of the experiment? Are you grateful for the changes or out for revenge? Do you remember what was done to you, or is it a mystery? How much of your life before the experiments do you remember? Did you even have one, or were you created by the experiment, making you an artificial being?
Ability Score Increases: +1 to Constitution and one other ability score.
Skill Proficiencies: Choose two from Arcana, Medicine, and Religion.
Tool Proficiencies: Alchemist’s Supplies or Thieves’ Tools
Suggested Equipment (Cost 4 gp): Manacles, rags, sledgehammer
Feature: Experimental Instincts. Your time being experimented on gave you a sense for what various strange things can do. You gain an expertise die on checks to identify unknown substances or devices and their purpose or effects (without using them). If there would normally be some penalty for failure when attempting to use something you have identified (such as damage, being poisoned, or other detrimental effects), you are spared from those effects on a failed roll.
Adventures and Advancement. There are a lot of experiments going on in the world. If you contribute to enough beneficial research and/or stop enough dangerous research, you may gain an assistant to aid you, gaining the services of an inexperienced follower of the Apothecary, Diviner, Healer, or Sage types.
Connection and Memento. Roll 1d10, choose from the lists below, or make up your own.