NPC Packs

I've seen that some people in youtube videos have extra animals, or enemies and I was wondering where people get them, does anyone know?

 

It's called mods. They can be found at www.minecraftforum.net

 

There's this awesome mod called Mo's Monster mod. It adds birds, bears, ogres, wraiths to the game. The mod isn't patched at the moment though and is out of date.

 

For working mods, just go to http://www.minecraftforum.net/viewforum.php?f=1032&sid=f31b0e1abf31259baea8487ca9133779