Adamantine/ Mithril

Adamantine
Adamantine increases gravity this works exponentially so if you have a sword made of Adamantine it will have little effect besides making the item itself heavier A massive amount of adamantine will make it possible to attract large objects and even reverse gravity in small areas.

• Adamantine armor
Can be any Medium or heavy armor, but not hide. While you’re wearing it, any critical hit against you becomes a normal hit. additionally, if the armor has a strength requirement it is increased by 2 and scale mail, breastplate, half-plate, and ring mail gain strength requirements of 11,11,11, and 13 respectively.
• Adamantine weapons
Melee weapons and ammunition made of or coated with adamantine are unusually effective when used to break objects. Whenever an adamantine weapon or piece of ammunition hits an object, the hit is a critical hit. If a weapon made of Adamantine normally has the light property it loses it. if a weapon normally has both the light and finesse properties it cannot be made of adamantine.

Mithril
Mithril decreases gravity this works exponentially so that if you had a weapon made of Mithril it would have little effect on the surrounding area. A massive collection of Mithril consolidated in one place will begin to float even carrying a proportional amount of additional weight. this is how the floating islands above Gro-Daric's Pale tower mountains stay in the air, this effect works almost like a magnet repelling away from the ground with a larger concentration of the metal having more force to repel away so the larger the island the more altitude it is capable of. this will be counteracted by weight being added so if a large enough structure is built on one of these islands it will lose a noticeable level of height.

• Mithral armor
Can be any Medium or Heavy armor, but not hide. A mithral chain shirt or breastplate can be worn under normal clothes. If the armor normally imposes disadvantage on Dexterity (Stealth) checks or has a Strength requirement, the mithral version of the armor doesn’t.
• Mithral weapons
An item made from mithral weighs half as much as the same item made from other metals. if a weapon normally has the heavy property it loses it. if a weapon normally has the heavy property and deals bludgeoning damage the weapon cannot be made of Mithril If the weapon isn’t Heavy, it becomes Light. If it is already listed as Light it gains the Finesse property. If the weapon is Two-Handed it is now instead Versatile. Mithral ammunition is too light to be effective.

Reaction
If these two metals come into contact there is a chance of a sudden violent reaction repelling the metals and anyone holding or wearing either piece. If you make an attack roll using a weapon made of adamantine or Mithril against an enemy wearing armor made of the opposite metal the enemy is treated as having a +2 AC as the two metals slightly repel each other like they were magnets with the same pole, however, if your attack roll misses by no more than 2 then both the target and the attacker must make a contested Strength saving throw. if the target loses the contest then they take half the attacks normal damage as force damage and are pushed back 10' if the attacker loses the contest then they take force damage equal to their attack modifier and their weapon is knocked out of their hand falling 10' behind them (if the weapon cannot leave there hands for magical or mundane reasons than they take double damage instead) this reaction creates a loud boom that can be heard up to 300' away