User blog comment:The Lost Marbles/Seles, the Shooting Star/@comment-5663427-20140803120524/@comment-25193301-20140803165412

Q: Ezreal's Q only costs 40 mana at rank 5 and lowers its own cooldown to like 2 seconds on-hit or thereabouts, so I think the cost is fine where it is. If anything, Redshift could stand to cost a bit less.

W: I was considering making this a scaling value,. Putting it on par with Furor at rank 5.

R: Remember that Supernova deals damage over time, so it continually procs Asterism's passive. The scaling slow also gives it a quirky execute-style usage, especially since its own damage will continue to raise the slow higher on enemies, making it harder to escape. Unless you're Lucian or something with BS mobility, but there's really not much accounting for that. Though I did consider a bonus where detonating Blueshift within the Supernova would trigger a root instead of its normal slow.