Combat inventor

Someone who invents stuff.

Bonus proficiency

Upon choosing this archetype at 3rd level you gain proficiency with smith's tools and tinker's tools. You can use these tools to craft ammunition, repair weapons, even draft and create new ammunition (DM's discretion).

Arcane smith

Also at 3rd level, you gain the use of an uncommon magic item you created and finished during a short or long rest after leveling up. You are assumed to have worked on it during your leisure time up to this point. You create an uncommon magic item of the DM's approval. At 7th level, you create a rare item; and at 15th level, a very rare item.

Inventor's satchel

Once you reach 7th level, you create an inventor's satchel. As an action, you can reach into the satchel and take out one of the following: a vial of green slime, a smoke stick, or thunderstone.

Green slime: You take out a small vial of green slime and throw it at a target within 30 ft, or 60 ft at disadvantage on the attack roll. Hit: The vial shatters on the target, covering it in green slime, dealing 5 (1d10) acid damage, and 1d10 acid damage every round until the target or someone else uses an action to scrape it off. Miss: the vial shatters and covers a 5 ft. square area within 5 ft. of the target.

Smoke stick: You take out a stick billowing a thick plume of smoke. You can either carry it or throw it up to 60 ft. Either way, the area within 20 ft., including around corners, is heavily obscured by smoke. The smoke disperses after 1 minute, or after a strong wind disperses it.

Thunderstone: You take a small, glowing yellow stone and throw it up to 60 ft., where it detonates into a shockwave. All creatures in a 10 ft.radius of the point of impact must make a DC 15 Strength saving throw, being pushed back 15 ft. and knocked prone on a failed save. On a success, they are only pushed back 5 ft. and aren't knocked prone. You can also detonate it in the air, any time before it hits something. 

Inventor's genius

Starting at 10th level, if you spend 1 minute or more trying out, touching, or otherwise using an crafted item, though it doesn't have to be you who crafted it, you learn all properties of that item, even if it is a magic item. 

Great crafter

At 15th level, you have learned how to improve a weapon's power and effectiveness. During downtime, you can spend 1 week of crafting no less than 8 hours a day, regardless of help, and 50 gp to improve a non-magical weapon into a +1 weapon. You can also spend 2 weeks and 100 gp of materials to improve a +1 weapon into a +2 weapon, and 3 weeks and 200 gp to improve a +2 weapon into +3. You cannot improve weapons with any additional properties.

Master maker

At 18th level, your mastery of craftsmanship becomes apparent, because you have finish making a non-unique legendary item of the DM's approval.