These critical effects for cantrips are designed to be used in conjunction with your standard critical rules. Whether you use the standard critical rule, crunchy criticals, or some other variation, these additional effects will stack alongside them without breaking the game.
When you see Critical Hit, it means that the spellcaster rolls to hit, and the critical effect is triggered when they roll a 20 on a d20.
When you see Critical Fail, it means the target of the cantrip needs to roll a saving throw against the effects of it, and the critical effect is triggered when the target rolls a 1 on a d20.
This document contains 33 Critical Effects you can add on to all existing cantrips that call for a roll to hit or saving throw.
- from the publisher's blurb