Unique: Your spell damage will slow the target by 35% for 1.5 seconds (15% for multi-target spells, damage-over-time spells and spells with a cooldown time below 3 seconds).
Spammable single-target spells only apply the 15% slow. The reason for this, as stated by Guinsoo, is: "We don't want a 35% slow that can be reapplied indefinitely." Currently, the only ability affected by this is 卡西奥佩娅的Twin Fang. Conversely, 卡尔萨斯的Lay Waste, despite both being an AoE spell and having an extremely short cooldown, applies the full slow, but only if it hits a single target.
The general rule is that spells with a base cooldown of less than 3 seconds will apply only the 15% slow.[2]
Rylai is the name of the Crystal Maiden hero in DotA. Rylai specialized in using ice-based crowd control abilities to stun and slow her opponents. The icon for the Crystal Scepter is almost identical to the icon for the Crystal Maiden's Brilliance Aura ability.
Slow duration increased to 2 seconds from 1.5 seconds.
It will now trigger on dealing non-periodic spell damage, instead of spell hit. This means that spells like Destiny or Time Warp, which previously triggered the effect, won’t anymore; however, Rupture will now slow on dealing damage instead of on the initial cast, Powerball will now trigger the effect when you hit units, etc.
Slows from items (Phage, Frozen Mallet, Rylai's Crystal Scepter) will no longer stack. The largest slow will take effect until duration wears then next largest slow will take effect if it’s still active.
Passive: After a spell cast, your champion's next basic attack reduces your target's movement speed by 35% for 2.5 seconds. This effect can only occur once every 6 seconds.
Frozen Mallet.
编辑
卡西奥佩娅的
Twin Fang. Conversely, 
卡尔萨斯的
Lay Waste, despite both being an AoE spell and having an extremely short cooldown, applies the full slow, but only if it hits a single target.
