Should DnD combinations commute?

[hamishspence]

When I saw your question I thought of half-troll dragons and half-dragon trolls. They're very different.

Might be rather interesting to see a troll-dragon villain pairing, with their children being a mix of both- warty green dragons, and winged, scaly trolls.

I wonder how many "odd pairs" one could do?

Half-dragon fiend + half-fiend dragon
Half dragon celestial + half celestial dragon

Half-dragon fey + half-fey dragon

And with Savage Species, though I'm not sure if its supposed to be interpreted this way:

Gelatinous dragon + half-dragon gelatinous cube.