Rylai's Crystal Scepter

Rylai's Crystal Scepter is an advanced item in League of Legends. Rylai's Crystal Scepter is the counterpart of the for casters: dealing ability damage slows the target(s) for 1.5 seconds.

Recipe

 * (435g)
 * (860g)
 * (1110g)
 * 700g

15% slow
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.

Synergy
All champions who rely on spells for damage synergize with Rylai's, as the Health gives much-needed survivability, the ability power increases damage output, and the slow lets one get more time on their target.

Rylai's is a good addition to almost any caster's build, though there are a few champions who don't need the extra crowd control. For those, is a better item as it provides health, mana, and ability power.

Trivia
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.