This is the best program for doing lots of editing to the MUL files. It’s a bit tricky to figure out at first but it’s by far the best program for editing everything. It can view and edit all of the MUL files.
MulPatcher is kind of like a Swiss Army Knife. It is capable of patching nearly all MUL files, even if the support for advanced animation MULs (anim2.mul etc) is somewhat bareboned. But this seldom affects it's useability, because most people only patch the original anim.mul or even verdata.mul.
What has to be mentioned is a rather annoying bug in MulPatcher. It only remembers one path to the files it's using. So if you load for example art.mul from your UO directory, then insert a graphic item from another location and finally try to save the arts mul, MulPatcher will offer you the directory with the graphics at first. This would not be a problem because you can change the target directory. If not sometimes mulpatcher tries to open the destination file (in this case art.mul) BEFORE you clicked on "save" in the dialog - and this will lead to a complete crash of the program. Image you inserted dozens of artworks in the past two hours, and now it will be completely lost. So as a workaround you should always store all needed files together.