while playing a mod called DarkRPG a looked around and found under gameplay drops a lootpool called Chungus Bartering Gameplay drops. which made me hunt the creature down and try to barter with but after throwing a bunch of items in front of it but no progress which brings me here.

Can you barter with big chungus and if so with what?

There is no information about being able to barter with them in the wiki.

You give them chungus emeralds by right clicking on them with it. You get the emeralds by killing them.

Wiki is outdated. They can pick up Chungus Emeralds, but they won't go out of their way to pick them up. You can right click them to trade directly, halting them for a limited time.