High Voltage

Mechanist Technique: 11th level You are used to working with electronics and have learned to increase their potency, while becoming inured to their dangers. You gain resistance to ion and lightning damage. Additionally, whenever you deal ion damage to a creature, you can spend a tech point to force the creature to make a Constitution saving throw. On a failed save, it is stunned until the end of your next turn.

Granted by Mechanist Technique (Companion) at 11th level.