Arctech Tinkerer

You are proficient in the Engineering skill and either smith’s tools or tinker’s tools.

Choose one gadget from the list available to the Gadgeteer fighter. You have a basic codex with instructions to create that gadget. You can also add more gadgets to your codex by learning from other inventors, typically by spending one day of down time with that inventor’s aid and spending 100 gp for the necessary materials to tinker.

Whenever you complete a short or long rest you can prepare one copy of any gadget you know how to make. If you prepare more gadgets, your previous gadgets cease to work. If you are also a fighter with the Gadgeteer archetype, the gadget from this feat stacks with the number you can prepare from your class.

Most gadgets can only be used once, then become inert. If a gadget calls for a saving throw , the DC is 8 + your proficiency bonus + your Intelligence modifier.

You also can cast a special version of find familiar as a ritual, requiring 10 gp of arcanotechnological parts, which must be assembled together into a pet contraption. 

The contraption uses the same list of beasts as find familiar , but it is a construct instead of a beast. It is resistant to bludgeoning, piercing, and slashing damage from nonmagical weapons that aren’t adamantine. It is immune to poison and psychic damage, and cannot be charmed , exhausted , frightened , paralyzed , petrified , or poisoned . It has darkvision out to 120 feet and understands your languages, but cannot speak. If the contraption is reduced to 0 hit points, you can repair it by using this ritual again.

You can spend an action to place a gadget into your contraption, or to remove or swap a gadget you had previously integrated. Even if you can make more than one gadget at a time, your contraption can hold at most one. The contraption can then spend the appropriate action, bonus action, or reaction to use the gadget, using your attack bonus or other stats to determine its efficacy.