Crimson worm

The crimson wrom is a boss that would be suggested to be fought right before the wall of flesh due to the crimsified phase blade it drops

Here's how you summon it: make a world with the Crimson (unless that's your main world) then make a world with the corruption (again unless its in your main world) then get worm food and a bloody spine and 10 ebonstone to make the bloody worm food then use it in the Crimson while preparing for the goblin army