Hi,
I bought Mugen yesterday, and as I've searched through this forum, my mobo was incompatible because of the non-standard retention. It was written
Biostar TA690G AM2 (Original AM2 retention is non-standard).
So I've ordered my cooler with Thermalright retention kit which cost me 10$. I've received my package, opened it. Before installing new retention kit I've tried Mugen if it's really incompatible. But I heard the clips sound and it was well fit on the mobo's original retention. So I didn't need to install the retention kit I bought as an extra...
For your information...
PS: I can send photos if they're needed. 