How can i create a new monster from scratch?

I saw in the doom2 wad file that the monsters are just a bunch of
images. So if i see this correctly to create a new monster you only have
to create a image of the monsters front, back and side view and moves for things like walking and attacking and write some code, right? Are there any good programs for this?

Decorate is what you need to write an file for your monster, notepad is an good program for making this or do it directly in xwe select new and type decorate and make you script in that.

Its not easy to make new monsters from scratch unless you have very good graphics skills, most monsters I've seen are based on original doom monsters and I think you should start easy with an imp or something and make an script for that getting the script to work is hard enough as it is at least for me it was.

Only Zdoom(doom in hexen format) or Gzdoom format supports decorate maybe others as well but those two I am sure of.

http://www.zdoom.org/wiki/index.php?title=DECORATE

hmmmmmm.still did not find the right program.

Use something like window's paint or paintshop pro for creating graphics. Its usually easiest to keep all the different frames on one large image so you can see how they relate to one another.

Use XWE for exporting images from doom and importing images into your wad. Use decorate for coding the monster. Sprites can't be loaded anywhere in the wad, they must be between the SS_START and SS_END markers.

Making the images is the most time consuming part. Download something like the monster resource wad and reverse engineer it to see how all this should look.