Tarrobe

Bhall: Lord of Murder
Pros: Get Slayer form that heals with every attack and causes the target to bleed (+200hp, -5AC, 4 attacks, no spellcasting)
Cons: You want to kill everyone

Jergal: Lord of the End of Everything
Pros: You can't truly die in this form, only Wish can
Cons: You want to see the end of everything

Kelemvor: Judge of the Damned
Pros: Gets +1d8 for every sin the target has done
Cons: For every kill you do, you must save a life

Loviatar: Madien of Pain
Pros: +1d12 force for every 10% of hp lost to your max hp
Cons: after you will lose this form, you suffer a week of agony

Maliketh: Ruler of Destined Death
Pros: Each weapon attack will reduce the target's hp by 10%
Cons: He will come for you

Myrkul: Lord of Bones
Pros: Assume the form from Baldur's Gate 3
Cons: You want your friends' bones and after the form is finished, your bones are gone for a few hours

Raven Queen: Matron of Death
Pros: Able to alter the memories of anyone, more important the memory, higher the DC for you to succeed
Cons: Chance for you to lose an important memory

Shar: Mistress of the Night
Pros: +2 AC, Lie without any checks, assume a copy of a previous enemy
Cons: You will lose what you hold dear most

Vecna: Maimed God
Pros: Gain the abilites of his hand and eye
Cons: Lose a spell slot or more