yo ucan actually fight bosses again(for more purple items). The Giant Slime on Level 2 spawned right beside the town teleporter, so after i completed the level 2 map(finished exploring it) I went back to town, healed up, went back to level 2 and kept on fighting the giant slime to get more items :) +1 if this helped you
does losing your powerups when you bump into red circles count as "using a powerup" for the not using powerup achievement? i technically didn't use them...
For those who completed story mode and don't want to lose their saves, please don't use a new game as it will overwrite the Story mode! I tested this again and creating a new game will ALWAYS overwrite your first save!
to do it in 11 days, you only have to buy the artillery(to kill the red giants) and the rusty nail upgrade(or to be even faster, dont buy this upgrade) then just repair for every 5k you get