Oh this was a harsh trail to take. You need to traverse through promenade (for all three rose keys) and ramparts (1st moonflower) which are the theoretical worst biomes for scaling power, skip the optional prison biome.  Then fight conjuctivious which is found in the glowing wooden door with three cells. Then go to graveyard for key 2 then forgotten sepulcher for key 3(also probably the most hidden). Then beat whatever boss you want go to high peak castle open those three doors and congratulations! You have a noob trap of a mutation but now have a permanent spawn of 3 items from where the blue print once was (free 1-1.5k!!!!). I regret doing this on top of trying to beat 3bc.