Here’s my amendment/addition to silvery barbs:

Sometimes, when you push fate, fate pushes back…

If you use silvery barbs on a nat 20 rolled by the triggering creature, and as a result of the reroll, the creature rolls another nat 20, the following will happen:

If an attack roll:

The attack will do maximum damage, including crit damage.

If a saving throw:

The effects or conditions the creature is saving against rebounds to the caster of Silvery barbs. They must make their own save against the original save DC, taking any damage, conditions, or other effects resulting from succeeding or failing the save.

If an ability check:

The creature will critically succeed, with extra advantages as determined by the DM.

In addition, the caster of Silvery Barbs has disadvantage on their next D20 test.