Why does 3v3 have the item Nashor's Tooth?

Twisted Treeline.

Nashor's Tooth is removed. Vilemaw's Stinger is added.

Vilemaw's Stinger, 20AD,60AP,45% attack speed, 5% movement speed, Passiv: When kill a minion/monster you gain 10 hp and 10 mana back. Unique Passiv: Every time you auto attack a minion/monster/champion you deal 10+x dmg per sec (1 dmg lv 1, lv 18 18 dmg) for 3 sec. Scales with 10% of your ap and 5% of your ad. passiv: inflicts grievous wounds.

3250 gold. how to build it: Stinger 1000 gold. Executioner's Calling 800 gold. Ather Wisp 850 gold. 2650 plus 600 for the item.