Special materials

Adamantine weapons (10 pieces of ammunition)

Normal hits against objects are critical hits.
+500 Gp cost.
(pg 78 Xanathars)

Adamantine armor
Critical hits against you are normal hits.
+500 Gp cost.
(pg 150 DMG)

Mithral armor
Does not impose disadvantage on stealth checks.
No strength requirement to wear.
+500 Gp cost
(pg 182 DMG)

Mithral weapons (10 pieces of ammunition)
Half normal weight.
+500 Gp cost.
(House rule)

Silvered weapons (10 pieces of ammunition)
More effective against certain enemies.
+100 Gp cost.
(pg 148 PHB)

Darkwood weapons (10 pieces of ammunition)
Half normal weight.
+500 Gp cost.
(House rule)

I wish you the best in all your violent endeavors.

–Argo