Lockboxes should be tiered. Blue lackbox's key dropped relatively early by a boss Green lockbox's key - moderately difficult. Red - hard to get, late-game superboss. Eternium box - - key is at the end of campaign's alst mission, in Hardmode only, using it on a Blood Temple releases a Boss Rush wave. Diamond - $1 per key, replaces token, gives a random Store item - such as a skin, pet clothes... Blue/green/red lockboxes could contain pet versions of the bosses dropping those keys as the rarest rewards. Boss Tamer is an achievement for getting pet versions of all boss types.