1)Extract the war3map.w3u from your map using your favorite MPQ editor.
2)Open World Editor and click File> New map.
3)Go to the object editor (The helmet).
4)File> Import Unit Settings. point it to the extracted .w3u file.
5)Got to Undead> Melee,> Units and down to the aggressor.
6)Scroll down to the Art-Tinting color. The values are 0, meaning black. Each value can go up to 255. This adjusts your color. Basically what owner said.
7)Go To Art:Scaling Value. You can change the value to 0. Meaning it should be one pixel(I think?). this may help the lag, but I'm not sure if the model is still being rendered with animation, but on a molecular scale.

8)Got To Art:Model file. This is the animated figure you see in black on your screen. You can change this to whatever you like. Change it to a non-animated model, like a tree stump if you want. I would try a Wisp first, small model and minimal animation.
9)Save map. Click file, export unit settings.
10)Import the file into your favorite MPQ editor. and save the map. I'm not good with the import and save process, so if it doesn't work you may need a little help from owner.
11)Load map into Frozen Throne to test any changes to the map you may have tried.
12)If it works, rejoice. If it doesn't work, go back to 6) and try a different model or scaling or whatever.
Don't look at Art-Target on the picture. I only clicked there before making a screenshot.
