When this Equipment enters, create a 1/1 black Assassin creature token with menace, then attach this Equipment to it.
Equipped creature gets +1/+0.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)
If the triggered ability causes two Assassins to be created (due to an effect such as that of Doubling Season), Headsplitter becomes attached to one of them.
No player may take any actions between the time you create the Assassin token and the time Headsplitter becomes attached to it.
The Assassin token that you create enters the battlefield as a 1/1 creature. Any abilities that trigger when a creature with a certain power enters the battlefield will see the token enter as a 1/1 creature. Static abilities that affect the Assassin's power and toughness may change this.