Guide on adding a new model, animation, and creature to HoMMV

Well, you can buy it, although it's not a certainty. It's probably impossible to get a legal copy of version 6.0 anymore.
But theoretically, I think it might be possible to rewrite the scripts we have to work with a different program? But that would probably be quite difficult.
In any case, I was using Blender as an example of professional (since some studios use it) and free 3D modeling software.
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Forget about Blender; it doesn't support gr2 export. Heroes is designed to work only with gr2 files exported from Maya (even if you find a gr2 export for 2.5.0.5 for 3ds Max, they won't work correctly, although that needs to be tested). And how do you plan to rewrite the mll plugin, Granny Export, which is specifically designed for Maya 6.0? And no, you can only buy versions starting from 2011, and who would think of selling a license for an antique version from 2004?