Drachenschrei

You can use a bonus action to choose one ally other than yourself within 60 feet of you who can hear you. That ally's critical hit range is extended by 1 for the next minute or until they land a critical hit, whichever happens first. If the ally is Dragon-type, double the critical hit range extension. This bonus does not stack.

A critical hit range extension of 1 means a critical occurs on a natural 19 or 20.

Auf höheren Stufen: The critical range extension changes to 2 at level 10.