Cloud Dragon

The blocking clause does all the balancing work: a 5/4 flier that can only intercept other fliers has given up the defensive half of combat entirely. That trade is Portal's design philosophy in miniature. The set used a simplified rules vocabulary aimed at newcomers, and one of its recurring tricks was a flavor cue that doubled as a balancing lever (clouds drift past the things below them rather than standing in their way). Framing the limitation that way let the designers hand out a big evasive threat without it also working as an air-and-ground wall. The math reads as pure offense: six mana for five power in the sky, with no pretense of holding the fort behind it. That is how Portal kept its creatures legible. A card either attacks or defends in a clear lane, and this one attacks. The bump in the rate (more body than a comparably costed flier with full blocking rights would carry) is the compensation for ceding the ground. It is a teaching-set artifact more than a constructed object, but the underlying idea, paying for raw evasive size by surrendering flexibility, is a balancing trick that has reappeared in plenty of later fliers under less explicit flavor cover.