There are currently over 500 unique enemies in Terraria across all platforms. This is more than the 329 characters known as enemies as this list not only includes distinct enemies, but also includes the variations of enemies such as Zombies and Slimes, the individual sections of segmented enemies like Wyverns, and non-typical enemies such as critters, projectiles that can be damaged such as Water Spheres, and friendly / town NPCs.
Many bosses and some non-bosses have unique attacks that increase or decrease their damage and defenses throughout a fight. See each enemy's page for more details.
Some enemies have separate ranged and melee damage values. Ranged damage values are italicized. See each enemy's page for more details.
A small number of enemies are effectively or entirely immune to damage and can never be killed by the player.
A very small number of enemies are currently unspawnable, but may potentially be spawned by third-party means and may be fully added to the game officially in future patches.