How does the artifact shop work?

[makaronii]

I don't know what boss fragments I can use to buy the artifacts and how it works?

 

[Damiceraj]

all that you can stack

 

[SKY_]

Make sure to use stackable boss drops and also doesn't use (boss souls,Boss fragments ,etc.)

 

[Wizzardness]

It works only with boss drops, and not Boss fragments, there is a confusion, i was there also
Boss drops are items that below them are written something in the lines of "This item is dropped from <Name of boss>".
Boss fragments are used to upgrade spawners to Prestige version of them.
Boss Souls - are boss keys that u can open in Boss world by following up the stairs on the left side before the "portal" that brings u to first level boss area.