Support. Contest the first rune using Crystal Nova and use it off cooldown on enemy laners, it is extremely strong early on. Use Frostbite to set up early kills when your carry is ready. Use Crystal Nova to push lanes and farm creeps after the laning phase is over. Consider buying Blink Dagger before Boots as Crystal Maiden is extremely slow regardless. Use Glimmer Cape to become invisible before channeling your ultimate (hold R to channel). Get your team to kill Tormentor at minute 20 so you can get Aghanim's Blessing, which gives you the escape ability Crystal Clone.