The UA Centaur (from Unearthed Arcana: Centaurs and Minotaurs) has the Charge ability:
Charge. If you move at least 20 feet straight toward a target and then hit it with a melee weapon attack on the same turn, roll the weapon’s damage dice twice and add them together. Once you use this ability, you can’t use it again until you finish a short or long rest.
How does this ability interact with a critical hit? Does it triple the weapon damage or quadruple it?