When I used the suspicious eye to summon Eye of Cthulhu at night, he wouldn't spawn. Is it a bug or do I need to do anything else? I have full health in red hearts, 13 defense, and I'm using a tungsten broadsword.
You can spawn Eye of Cthulhu with a Suspicious Looking Eye only if all of the following conditions are met:
- It's nighttime (you should summon it at nightfall anyway since it will disappear at dawn)
- It's not raining
- You are not fighting a summoned Eye
Your item won't be consumed otherwise and nothing in particular will happen.