May I announce also a default reaction, please. Zrukz will never use reaction to make attack of opportunity, instead he will use his reaction any time
1) any enemy score nat 20 on attack roll against any PC
2) enemy pass a saving throw against lvl 1 or above spell cast by any PC that only target single enemy
[ +- ] 1: Silvery Barbs (Cha)
Casting Time: 1 reaction, which you take when a creature you can see within 60 feet of yourself succeeds on an attack roll, an ability check, or a saving throw
Range/Area: 60ft.
Components: V
Duration: Instantaneous
Source: SACoC, pg. 38
You magically distract the triggering creature and turn its momentary uncertainty into encouragement for another creature. The triggering creature must reroll the d20 and use the lower roll.
You can then choose a different creature you can see within range (you can choose yourself). The chosen creature has advantage on the next attack roll, ability check, or saving throw it makes within 1 minute. A creature can be empowered by only one use of this spell at a time.
For simplicity I will by default choose my own PC as target of the second part of spell description (advantage)