Signature Cantrip

You have spent an extensive amount of time studying and practising a singular cantrip. You gain the following benefits:

Increase your Intelligence, Wisdom or Charisma by 1, to a maximum of 20.

If you cannot cast spells outside of this feat, you may learn one cantrip from any spell list. Your spellcasting ability modifier for this cantrip is the ability score increased by this feat.

Choose one cantrip that you know. You gain the following benefits when using that cantrip:

Your signature cantrip does not count towards your known cantrips. If you weren't able to cast spells before gaining this feat, this does not apply.

If your signature cantrip has a casting time of 1 action or less, you may cast it as a bonus action a number of times equal to your proficiency bonus per long rest.

If your signature cantrip requires an attack roll or saving throw, you may add your proficiency bonus twice to your attack roll or spell save DC when using this cantrip. 

Your signature cantrip's range is doubled. If your cantrip has a range of Touch, its range becomes 30 feet.

If you signature cantrip's duration isn't Instantaneous, its duration is doubled.

Mastering a cantrip may provide other benefits, depending on the cantrip. Work with your DM to decide other things you might be able to do with your signature cantrip. For example, somebody with Mage Hand as their signature cantrip could be able to use the Arcane Trickster's Mage Hand Legerdemain feature.