I heard somewhere that if you fish alot during pre-hardmode for crates and open them in hardmode, you'll get alot of hardmode ores, so i tried this and opened 109 crates but
Aftermath of me saving over 200 crates and opening them all in hard mode haven't even broken any demon alters : r/Terraria
I Opened 1000 Of Every Crate In Terraria To See Which Is Most Profitable - YouTube
New Terraria 1.4 crates (from fishing, duh) in 3 minutes... - YouTube
Terraria: Every Kind Of Crate & Where To Find Them
Steam Community :: Guide :: Best way to obtain Crates
Steam Community :: Guide :: Best way to obtain Crates
Crates Fishing (for hardmode ore) | Terraria Community Forums