There are two Blender add-ons you can use to export DTS files, which is one of the two file formats the Torque Game Engine (MB's engine) uses for 3D models (the other being DIF, used for platforms and general level parts, DTS is for more complex geometry like powerup models and marbles).
One of the add-ons is only compatible with Blender up to 2.49 I believe, but is much more complete. I don't know much about that one, RDs Empire can probably help out with that.
The other one
works with the latest version of Blender but doesn't have all of the DTS features, although it's good enough for a new marble model. It can also import DTS files, with the exception of the ones that were specifically made for PQ's levels (dunno why it can't import those).
Most of the questions you may have about this add-on should be in the FAQ, but feel free to ask me if you need help. Here is some advice (the first three points apply to the other add-on as well):
- Don't use a collision mesh, the game generates its own collision for the marble. If you do, then the DTS' collision will be treated as a separate non-moving object so the marble will basically collide with itself and hang in the air.
- The default marble has a diameter of 0.4 units.
- I have no clue how PQ's marble reflections are affected by the DTS, but they might do something weird to it in-game. Whirligig or the PQ devs should be able to help with that.
- If, after exporting, the geometry is transformed incorrectly, you may need to apply the transformations in Blender before exporting. Only empties are able to have transformations and animations. You can parent meshes to those.
- Use the default Blender renderer.
- The name of a material must be set to the name of its corresponding texture, excluding the file extension (in fact, I don't think you even need to put the texture on the material in Blender).