Savant

You're usually not very good at things...except when you suddenly are.

• Choose an ability score for which you have a negative modifier. Whenever you make an ability check or a saving throw using that ability score, you can choose to treat that roll as a 20. You can choose to change the roll after you roll the die, but before the outcome is determined. 
• You can use this feature a number of times per long rest equal to the absolute value of your chosen ability score's modifier.
• You regain all uses of this feature after a long rest.