The mark of the cursed one

A mark is engraved on the characters chest. It beholds another soul. Due to a failed transmutation on the human  the mark has been damaged and therefore no longer contains the secondary creatures soul as efficient and reliable as before. This allows the creature to overthrow the main characters consciousness at given circumstances up to a point of full bodily control. This may only occur when:
- under stress
- heavy emotional impact
- adrenaline/blood rush (blood lust)
- DM says it happens

Actual Traits:

You are fragile but powerful. You gain the following benefits:

• Once in each of your turns when you deal damage to a creature, you can use your bonus action and roll a d10. You lose an amount of hit points equal to the number rolled, an increase the damage dealt by the same amount. If your damage affect multiple targets, you must choose only one to take the additional damage.

• You can choose to have vulnerability to all types of damage until the start of your next turn. Doing so will increase the damage of all your attacks against targets within 20 feet on the current turn by 5. On a critical hit, you deal 10 additional damage, instead of 5.

• Whenever you have less then a quarter of your total of hit points, you score a critical on a roll of 19-20 on your attacks

It's the Glass Cannon Feat -> I'm going to make some changes to give more options incl. scaling