Originally Posted by Hedgepig
I've read that slows from various sources stack, but does Rylais scepter stack with spells that have slow effects already? I picked it up on Nunu towards the end of a game the other day, and didn't notice a significant difference in slow amount. I could just be unobservant, or there might have been confounding variables (champions with ghost on etc).
I guess a way to confirm this would be to try it on Zilean (65% slow) and see if they stop dead for a short while, but I'm at work, and its only one data point.
They don't stack directly.
The highest slow will take effect. Once that one is removed or the duration is up, the next strongest will take its place if its duration is going.
Edit: Or thats the way it worked last I heard.