How many mobs are in terraria?

minecraft 1.9 is known as the "Lost Update". This means it was never fully released as 'Minecraft 1.9'. So here's a list of mobs from the current version as of now (v1.0.0):

1. Snow Golem
2. Chicken
3. Cow
4. Mooshroom
5. Pig
6. Sheep
7. Squid
8. Villager
9. Enderman
10. Wolf
11. Zombie Pigman
12. Blaze
13. Cave Spider
14. Creeper
15. Ghast
16. Magma Cube
17. Silverfish
18. Skeleton
19. Slime
20. Spider
21. Spider Jockey*
22. Zombie
23. Enderdragon
24. Herobrine*

*Spider Jockeys are glitched, it is a skeleton riding on top of a spider.

Enderdragon is a type of boss, which normally appears only once.

* Herobrine will appear because I witnessed it and you can lure him out

by killing a cow with red eyes.(It is Half Myth)

gogogp here, spider jockeys arnt glitches they spawn at a very low spawn rate, enderdragons only found in The End and hherobrine does not exists.

-gogogp :D