Horizontal cycle with Forteplazian Grounds, Moongrove Meadow, Heavenlake Waters, Irecliff Mountain.

Cool concept but it would probably work more smoothly as "you could choose the card and have opponent choose top or bottom".

Oh, the rare land cycle. I think I'm not totally happy with either, and that's kinda bad. For some time, the lands activated for (and the like), so it was okay if the effects were mixed. But most were effects so little it felt wrong to charge two mana.

In the end, there wasn't a strict rule about which colors should the effect be part of. This, for example, could go in either, I think. I do like how it works. Having you choose the card and then an opponent saying top or bottom would not work, because you would never get a good card back. As it is, you can slowly empty your graveyard (and put it on the bottom in case you don't need it) until your opponent chooses just what you want. The bad part is that it goes against black-green "fill your graveyard" kind of strategies.

I don't think that's much of a problem. So do Gurzigost, Battlefield Scrounger, Nantuko Tracer and so on. They're still useful in such decks. This is a really fun and interesting cycle, even if it is a little pie-stretching at times. I don't think this effect is much out of flavour for either colour.