Soul of Fright

One victory does not cover the shopping list. If you want everything this material feeds into you are going back for the same mech more than once, so build a stack of summoning items before the first attempt rather than mining ore between tries. The fight does not get harder on the second run, only more tedious, and having the summons ready is what keeps it from eating an evening.

These ignore gravity when they drop, which is more useful than it sounds. Kill Prime over the ocean, over a lava lake or above an open shaft and the drops sit exactly where they spawned instead of sinking somewhere you cannot follow. Sweep back through the cloud of them before you leave the arena, because nothing is going to move them.