I have not constructed a unicorn deck before, but The last unicorn sounds like a great one to base a deck or two around. There are green unicorns to choose from. Try some of these:  Prized Unicorn (from M10) , Noble Quarry (from Born of the Gods....I think, or at least from that Block) , Life's Legacy (M15). Also Opaline Unicorn (Theros) is an artifact unicorn and could go in any deck.  It's been decades since I have watched it, but doing a google search of pics from the movie makes me think it wouldn't be too hard to come up with cards for those decks. Could be fun.

It has only been play tested against my other Movie Madness decks. My brother and I have built decks based on some classic movies and pit them against each other. The cards can be from any expansion or block and the reason they are chosen are either for the picture, name or theme that go hand in hand with the movie. Decks are about 60 cards and usually have about one or two non-basic lands. I try to keep them within a 3 colour range, but sometimes we come up with a deck that is all colours. Since we don't own all the cards we often use proxies for the cards we don't have.  It's fun to pit them against each other, but I have never pit them against other people's regular decks.