Smashy Smashy Achievement
Use the Hammer Power-up ten times
The hammer power-up is unlocked on Episode 1: Level 13. Once you get the hammer in the level you will have to use it the first time to progress through the level. Please note that you can't replay the level to get the power-up again to boost this.
You will have no problem getting this while playing through the story. You can earn a hammer power-up two different ways. You can wait for the hammer to fill up while you play. It will take 50 popped pigs to fill the hammer power-up. Once it's full it will flash to let you know you have the option to use it. If you've increased the hammer's meter in a level and restart you will not lose any progress towards earning the power-up. Any of the Wall of Pigs levels are great for filling up the power-up.
The other way to get one is to buy it with the in-game currency. The more you have the meter filled the less you will have to pay.