The Eye of Cthulu(EoC) is probably the first Boss a new player will encounter during their adventure. This will tell you how to be prepared, the weaknesses, and strengths of this malicious eye.
Strengths: Is fast, has 2 forms, spits out slaves, and does extra damage in its second form.
Weaknesses: Has poor acceleration/deacceleration, is the weakest boss, easy for a ranged charachter(or magic) loses defense in second form.
Arena: 5-10 rows of wooden plat forms 10-20 blocks wide.
Weapons: Shurikens, a sword, and a bow.(a gun if you can get your hands on one as well)
The Fight! Just spam shurikens at the pupil and shoot your bow there too and you should win.