The Eye of Cthulhu is a pre-Hardmode boss and commonly one of the first bosses players encounter. It can be summoned manually at night with a Suspicious Looking Eye and may also appear naturally once early progression conditions are met.
Fight structure
The fight has two phases. The first alternates hovering, charges and Servants of Cthulhu; the second becomes more aggressive and charge-focused.
Preparation checklist
- Use an open surface arena
- Bring reliable mobility
- Carry enough healing
- Use a weapon you can aim consistently while moving
Source: Official Terraria Wiki.