Talk:The Twins/@comment-121.202.48.200-20120917071702/@comment-4674838-20120917073600

Yes, you should get full adamantite armor (preferably with melee helm for defense) before taking on any of the hardmode bosses. If you go to all the corruption and smash all the demon altars, it creates more ore. Best place to find adamantite is the roof of the underworld.

You will also need a top-tier ranged weapon such as a repeater, Crystal Storm, or Star Cannon. Megashark is also a great choice once you can get it. Without powerful ranged weapons, you will not defeat the twins or skeletron prime. (The destroyer however can be defeated with high armor rating + melee weapon such as the typically recommended Dao of Pow)

TL;DR If all you have is night's edge + dark lance + cobalt armor, you're not nearly prepared for hardmode (let alone hardmode bosses).