Then again, we don't get to see many modifications made based on MG Unicorn though. I suppose it's because many do not want to sacrifice the beauty of Unicorn's glittering inner frame and its ability to transform, or maybe Katoki-senshe's awesome mecha design needs no modification at all to look good. Some might want to try out the creative paint schemes posted on Toysdaily though XD.
Nonetheless, I would like to introduce to you, the best Unicorn mod work I've seen so far:
SD Gundam Unicorn, by Bluemoon from Koju.
Not transformable I believe, but it's very clear that many parts used for this SD work are from the MG version.
Very few people I know paid so much attention in modifying SD Gundam models. Bluemon is certainly one of them, and his work are not based on the regular SD Gunplas, but gashapon SD series which are much smaller. Just how did he complete this SD Unicorn is beyond my knowledge, but this Unicorn is definitely not his first work. He also completed some other awesome work like Exia and Hi-Nu Gundam. See more in his gallery.
This SD Unicorn is currently being auctioned on Yahoo! Japan. The first time I saw it (10 March), the bid started at 500 Yen, now (14 March, 11.32 AM) it has spiked to 20,500 Yen. By the time you see it, the bid might be (should be actually) much higher than that already. If you're interested as well, better move faster, because the bid is closing soon (16 March).
Images from Yahoo! Japan