Many thanks to the Animation Conversion Tutorial, which I couldn't write this without.TUTORIAL: How to make a 3D model be used by Diablo II
You should (and will need to) read the Animation Conversion Tutorial by Joel, Nefarius, and Alkalund first. It helps to get a grasp of the direction system and setting up the GIF and such. It is recommended you read this tutorial once-thru before following it.
Step 1: Make your model. Remember, It will be rendered small.
Don't make it so detail-crammed that it looks like a blob at a small size. When/if animating your model, take into account the fact that you can either do COF/animdata editing to use your own framecounts, or simply match the existing framecounts you will be replacing.
Step 2: Arrange your model for rendering.
Set up an isometric viewpoint (In anim8or, it's an ortho view.)
Now, the model will be rotated often. You need to set it up as such. (at least 8 times for monsters, 16 for chars, and such).
There are two options to make it rotate easily; pick whichever is easier in your editor.
Method 1: Rotate the camera between renderings, while keeping the angle isometric. Make sure that any lights you have rotate as well! The complexity of lighting makes this a more difficult method.
Method 2: Rotate the object (grouping it in a group or childing it in a null object first) between renderings. This one is easier for me.
The model should, at first, be facing direction 0 in Diablo II (Which is facing the bottom-left corner of the screen)
Step 3:: Render your model's first direction, first mode.
There are a few formats you can render in; they all end up about the same, although some lose color quality (Of course, Diablo II is a 256 color game, so it's somewhat moot of a point)
You can render it as a GIF, AVI (this is the only choice for some), or individual BMP's. The render size must be under 256x256, unless you're making a multiple-part animation, in which each part must be under 256x256. Realize that act bosses aren't much over 256x256 in total.Make sure you're rendering the whole animation and that everything is OK. It's best to preview your render before advancing to the next step. Make sure the background color ISN'T even close to anything in your model, and it should optimally be 170,170,170, or else your model might get semi-transparent and look horrible.
Step 4: Rotate your model to the next direction.
Rotate either your model or the camera so it faces the upper-left corner. This is a 45-degree change. It is now facing Direction 1 ingame. Render it the same way you did in Step 3.
Keep repeating step 4, rotating it each time, until you finish direction 3 (facing bottom-right). Then rotate it so it faces straight down (direction 4), and repeat the same steps, stopping again at direction 7 (right). For monsters, this is where you stop. For chacters and missiles, refer to the Animation Conversion Tutorial for the remaining directions.
Step 5: Assembling it all. Use GIF Movie Gear to open your first direction. (It may be import for AVI animations) Then, append direction 1, 2, 3, 4, 5, 6, 7, and so on. Before saving it as a GIF, check a few things. Is the framecount a logical number? (Such as 128 frames). If you get a weird framecount, such as 83, then something's wrong. Find what direction(s) are the problem, and fix them. Then (this next few sentances is in the Animation Conversion Tutorial) optimize the animation, with the following checked:
Shrink palettes (global and local)
Remove local palettes
Create a global meta-palette
Shrink frames to smallest needed rectangle
Then unoptimize, set transparent color, and make sure it's "Background Color" before drawing next image
Then save the GIF.
Step 6: Convert the GIF to a DCC.
Everything is set up in the GIF, so open CV5, save it as a .DCC, do offsets, and give it the right filename!
Step 7: Doing the other modes.
You will need to repeat steps 3-6 for any other animation modes you have.
Give it the right filename and folder, do Animdata/COF editing if needed (which is described in the Animation Conversion Tutorial), and check it out! Any assertion errors are, again, described in the Animation Conversion Tutorial. However, here's some errors specific to 3d modeling:
1) Part of my image is transparent!
This means that your background color and part of your image are two closely matched; they get merged in the palette as one entry.
2) My background ISN'T transparent!
You didn't set the transparency color properly in Step 5
3) My monster walks backwards or oddly!
The directions are arranged in the wrong order.
modder, very helpful. could this possibly be sticky material? 
