Cycle of creatures that share the same abilities - all with white ability have same ability, same with blue, black, etc. To match the Wedge colour Legendary creature cycle.

An aside: After having worked with Gatherer's feedback rating system for a while, I've noticed that cards that ask you to discard a card randomly almost always score terribly. A good way to see this in action is the comparative scores of Stormbind versus Coral Helm.

Stormbind deals 2 damage, but requires red and green to get started. Coral Helm gives +2/+2, but costs more to activate. 2 damage is generally going to be better than +2/+2... but not to an overwhelming degree. And that difference is going to mean something. But Stormbind has a rating of 3.776, while Coral Helm has a rating of 1.625.

That difference is pretty huge. And while I'm sure part of the reason why this is the case is because Stormbind is honestly a better card. I'm also pretty sure that part of the reason is that Stormbind was in tournament decks, so it gets respected, while Coral Helm was not, so it gets hated, hated, hated.

This is a lot of writing to put down on a minor point... and not even a point I'm trying to sell, eh? I mean, I think it's perfectly legit to use discard at random as a cost. I just think it's important to recognize how many players it actively upsets.