HARD MODE ACHIEVEMENT
For this achievement you need to obtain a rainbow rod which can be crafted.
The materials needed is,
-10 crystal shards (found in underground hallow)
-2 unicorn horns (dropped by unicorns in hallow surface)
-10 pixie dust (dropped from pixies in hallow surface)
-8 soul of light (semi-rare drop from any enemy in underground hallow)
-15 soul of sight (a drop the boss "the twins")
After getting everything it can be crafted at a mythril or orichalcum anvil.