I saw this happen a few times at Winter Fantasy. How about a crit when you roll doubles with advantage in DnD 5e? How about a feat for that?
Real Advantage
Gain the following benefits:
- Gain +1 to any stat to a maximum of 20.
- When you have advantage and roll the same number on both dice, it is considered a critical hit if you would normally hit with the number rolled.
Thoughts?
Throat Punch Games 
I like this one a lot. The only thing I’d change is removing this: “if you would normally hit with the number rolled”. If you run the math, this increases Crit Chance from 2 in 20 (because 2 chances to roll a 20) to 3 in 20. And it only takes effect if the Character has Advantage. Not OP or broken at all, in my mind.
Agreed.