Merchant

This is an unusual villager that would appear 3 times less often than a traveling merchant. But more often he spawns near some structures, perhaps even in a cave.

What if we could trade not only emerald, but also other metals (copper, amethyst, gold, diamond and even lapis lazuli).

You could trade copper blocks with him. Imagine that one unit is a copper block, then pennies are copper bars. Moreover, the merchant may require copper blocks of different oxidations for a variety.