Nothing is more solid than adamantium. Adamantium weapons ignore armor. Adamantium objects are unbreakable and combo with the Fighter’s parry ability.

A fairie that touches cold iron loses all abilities and resistances for a turn. They can smell it.

Mithral is light like cloth. Attack rolls made with mithral weapons are easy rolls but the damage die is one size smaller. Mithral armor doesn’t impede movement.

Platinum repairs itself after 10 minutes and as such combos with the Fighter’s parry ability. Platinum weapons ignore the resistances of aberrations as well as their horrid immortality.

Radium sheds light like a candle. It ignores the resistances of celestial creatures like angels and devils. After each adventure spent carrying radium, save or gain a mutation.

Silvered weapons ignore all the resistances of undead creatures and of creatures that are not in their true form.