(you can cast phantom steed once per short rest using dex as spell ability)

you have learned the dangers of westdeep, and the powers of the great nobles, so you learned how to steal, without dyeing due to the inevitable. 

Steady Hands

Starting at 3rd level, you can use the bonus action granted by your Cunning Action to make a Dexterity (Stealth) check, use your thieves’ tools to break a trap or open a lock, or take the [Tooltip Not Found] action.

Windglider

you decided to use westdeep to your advantage, and can now use it's winds (which travel with you), to glide 70 ft, and in doing so, take no fall damage. if 15 or more damage is done to you during the glide, you fall to the ground, but the damage with the fall is reduced be 15.  (min of 10 damage)

Westdeep stealth

when in dim light or darker, you turn invisible and can take the hide action to full effect.

Use Magic Device

By 13th level, you have learned enough about the workings of magic that you can improvise the use of items even when they are not intended for you. You ignore all class, race, and level requirements on the use of magic items.

Thief’s Reflexes

you use 2 opportunity attacks instead of 1.