Board Thread:New on Terraria Wiki/@comment-74.101.126.88-20121218114129/@comment-3157150-20130128091939

The Eye of Cthulhu is seen as the "base" boss in Terraria. After Hard Mode has been activated (by defeating the Wall of Flesh), The Twins can be summoned (using the Mechanical Eye). They have much, much more HP, attack, attack types, different movement patterns, higher defense, etc. Check each of the mentioned pages for their respective stat differences.