Halo 3 Decorators

To create custom decorators, you need at least 3 objects: A base, a node, and the object you want to make into a decorator. The base is usually a triangular object and, like the node, is mostly used to organize your variants.

The base triangle, the node cube, and the mushroom object.

You'll want to "Parent to Object" in the order shown here.
Make sure you name your objects with the same symbols and b_node.

Once you've imported your object, open the render_model and scroll down.
Change Vertex Type to Decorator and check "mesh is unindexed(do not modify)".

If you do not change the vertex type and check the mesh unindexed options,
your model will become distorted and triangulated:

To create variants, give the other objects the same name but change the number in the sequence.
H3's Tool importer is indecisive, sometimes it likes them having a b_node vertex group
and default default region, sometimes it doesn't.