Cool Card Design of the Day
3/16/2015 - I wanted to make {3} mana rocks whose bonus wasn't late-game value but mitigating the tempo hit you take playing them. The effects I came up with for these ally-color artifacts were specific to the colors they produced, so they needed to require one or both of those colors to play.
They could be {1}{W}{U} or {2}{WU}, but I realized this was actually a perfect place for twobrid. If you can already produce {W} and {U}, this card isn't fixing your colors, just accelerating, so costing two is fair. (Though, with the ETB ability, maybe not,) If you've got either, you can get it for the standard three mana. And if you've got neither, you can pay extra to get it anyhow.