Time Manipulator

You have a small amount of control over the weave of time around you. You can choose to manipulate it at the expense of yourself. 

• Whenever you or a friendly creature within 30 ft makes an attack roll, an ability check, or a saving throw, you can choose to use your reaction and roll an additional d20. You can choose to roll this additional die before or after the outcome is determined (within modesty). You choose which of the d20s is used for the attack roll, ability check, or saving throw.
• Using your reaction you can also choose to roll an additional die when an attack roll is made against you. Roll the extra d20, and then choose whether the attack uses the attacker's roll or yours. If more than one creature manipulates time in this scenario the weave itself is thrown into disarray and we will play that out in context. 
• Whenever you choose to use this ability you must make a Constitution saving throw DC 15. On a failure, you take 1 level of exhaustion. If you fail by 5 or more, you take 2 levels of exhaustion.