Arcane and Meteorite are the two tier-determining ores in Terraria.
Unrefined Bloodstone is found Underground, near lava pools, when mining with a Nightmare Pickaxe or better at any time of day. The chance is 0% during daytime unless it rains (the 15 minute duration doesn’t matter). It can also be rarely obtained from a chest inside the Lihzard Temple and crafted using charges from an Atmosphere Station. Otherwise it can randomly spawn when harvesting Ebonsand blocks on Floating Islands at Night with at least one Thumper installed nearby as soon as you have killed all available monsters within 3 screens radius (9×3 tiles) or cleared them out to increase spawning rate.
You need to have at least one Nightmare Pickaxe or better equipped in your hand or another hotbar slot. If it rains, first make sure to have the Pickaxe in your hotbar. Equip it if necessary, but do not switch slots otherwise, then click at least one Bloodstone ore block while being within 6 blocks of it. The message ‘ You feel an evil presence watching you ‘ will appear once every Bloodstone ore you mine. Keep mining more Bloodstones until the occurrence rate of ‘ You feel a strange chill ‘ appears. Then stop mining the Bloodstones and fish for Ice Mimics in water while being within 6 blocks of at least one Ice Block . It spawns 1-3 Mimics, giving you 1-3 Nightmare Pickaxes.