Tattered Cloth

This is the on switch for the Goblin Army. Turn enough of it into a Goblin Battle Standard and you can call the invasion whenever you are ready, instead of waiting for the game to roll one. That matters because the Goblin Tinkerer only appears bound underground after you have beaten an army, and reforging every weapon you own is locked behind him.

Goblin Scouts only spawn near the world edges, out in the outer third of the map on either side, and they run from you rather than fight. Walk the surface out there and keep something ranged handy so a fleeing scout does not escape offscreen.

They are uncommon enough that this is a walking job rather than a farming job. The upside is that the cloth is the only thing they carry that you need, so there is no sorting afterward.