I would look like Aurora Unit 313 (Perhaps looking similar to BoC in Terraria) That has 3 Eyes, Phazon Attacks, Ice Attacks, Dark Samus Echoes. 70000 hp with 2 phases. And could only spawn in Underground Corrupt/Crimson Ice.
15-20 Souls of Light (100%)
15-20 Souls of Night (100%)
1 Mechanical Eye (30%)
1 Broken Hero Sword (50%)
Frostbrand (35%)
Frost Staff (35%)
Ice Bow (35%)
5-10 Greater Healing Potions (100%)
77 Cursed Flames/Ichor
777 Ice Blocks (100%)
777 Snow Blocks (100%)
30-50 Phazon (100%)
Borealis (14%, a mid-hardmode sword with 70 base damage, can shoot projectiles of Light Energy)