The Gambler

Your patron is one who rides the highs of risk and excitement to bring about the opportunity for power or punishment. This being wants nothing more than to watch as you take every chance you can and seize every opportunity, whether it be beneficial or detrimental. Thus they have granted you powers that allow you to take gambles during you adventures to possibly give you an edge of your competition, or possible run you out of the race entirely.

Double Down

At 1st level, after when you make an attack roll or spell attack roll, you can choose to double down and roll a second attack roll or spell attack roll (NOTE: The second roll does not affect the first roll's chance of landing, meaning whatever you rolled on the first die is the number you must use). If the second roll is higher than the first roll you double the damage, if the second roll is lower than the first roll you only do half damage.

You can use this ability a number of times equal to your proficiency bonus, and regain all uses on a long rest.

Expanded Spell List

The Gambler lets you choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Call My Bluff

At 6th level, as a reaction you can choose a creature that just took an action and challenge them to a duel and both creatures roll 1d20. Upon winning this duel you can negate the effect of that action as if it never happened, however; if you lose the duel that action's effectiveness is increased by 50% (i.e.: attacks do 1.5x damage, healing spells or potions effectiveness is increased by 50%, etc).

This can be used a number of times equal to your Charisma modifier, and reset upon taking a long rest.

Poker Face

At 10th level, you can cast alter self at will and without using up a spell slot. Once per short or long rest, if you are caught by any means during the duration of the spell, it will immediately drop and you will be restrained for 1 minute and have disadvantage on Deception and Persuasion checks until the next long or short rest. However; if during the duration of the spell you can successful trick a single creature, you gain advantage on all Charisma based skill checks (Deception, Intimidation, Performance and Persuasion) until the next long or short rest.

Ultimate Gambit/Gambler's Intuition

At 14th level, you can create an gambling area around you and cause the creatures within that area to take a chance on every move they make. In a 25 ft. radius around you, any roll of a d20 must roll an additional d20 after it. If the second is higher, the effects for that roll are doubled, and if the second is lower then the effects are halved.
Additionally, during this time you can also pick any creature and gain insight into their capabilities. You are able to determine the current health, and effect/status/disease they are under, the AC, and any spell DC or ability DC (but not the details of the ability).

Once this is ability is used it cannot be used again until a long rest.