Its Cassiopia a fun character who is a fun assist to rack up the points.

Your first 2 items are nosuprise for a mage but you dont port back until 900 gold to buy your chalice and 1st boots. now your next item needs to be ethier the rod of ages or cooldown boots. If you grab the rod grab health item first. The rest is pretty self explanitory but I'll leave it upto you after the Void staff in my build order.

Dpending on what you want to do would determine your summoner spells.

Exausht and Ignite for an early gank

Clarity and Flash incase you want to mid

Or your own combnitation for this kind of hero

I like going mid with her that poison is a nasty Harass

If top or bot I suggest laneing with a Teemo or a Twitch to he you spam your E ability

Your ulti and your W ablity hit Akali while she hids in her Smoke bubble