You decide whether to pay {2} as the enters-the-battlefield ability resolves. If you do, you immediately create the Dwarf Berserker creature token and attach Dwarven Hammer to it. No players may respond to your decision to pay or not, and no player may take actions during this process.

The Dwarf Berserker creature token enters the battlefield as a 2/1 creature. Any abilities that trigger when a creature with a certain power enters the battlefield will see the token enter as a 2/1 creature.