new enemies

I am using db2 and would like extra monsters to use in the builder that i have seen from other wads. How can i acheive this?

You can't do that in-editor with Doom Builder or any of its branches, you have to get a lump editor like SLADE3, SlumpED (ugh), or XWE (double ugh).

There's plenty of tutorials out there on YouTube for how to make DECORATE monsters (search up "How to add custom monsters to Doom 2"), but if you're inexperienced then you might want to get your monsters from somewhere else like http://realm667.com/ or the Monster Resource Wad. Remember, don't go overboard and don't start mixing themes, otherwise your maps will be pretty cluttered and unprofessional.

If you don't want to map for ZDoom however, you'll have to learn how to use DeHackEd: it takes a lot of effort, but it means that you can have new monsters for any type of map.

1- Create your desired map, save, and exit the builder.
2- Go to these website to download custom monsters:
http://realm667.com/index.php/beastiary-mainmenu-136/doom-style-mainmenu-105
http://realm667.com/index.php/beastiary-mainmenu-136/heretic-hexen-style-mainmenu-137
http://realm667.com/index.php/beastiary-mainmenu-136/strife-style-mainmenu-173
3- Download "Slade": http://slade.mancubus.net/index.php?page=downloads
4- Install it and any required programs (if necessary).
5- Open Slade, then open your map.
6- Open another tab in Slade, then open the downloaded monster (usually is a wad file).
7- Copy the content of the monster files including sounds, decorate, sprites...etc, then paste them into your map file.
8- Now, save the new entries, exit, re-open the builder you're using; go to your object list, and you'll see something like "decorate" click on it to browse your newly added monster (you can have so many monsters as you want).
9- Place them, save, test...enjoy ^_^

Oh thanks alot guys, i especially appreciate the detailed walkthrough!