This achievement along with Area of Effects can be unlocked in Story Mode - 2 player.
You will obviously need 2 pads, but another person isn't essential. Start off on level 1, and make a 5 block match for the dynamite, then drop the barrel next to the other player. Boom, achievement. Then proceed to make matches of 4 blocks to spawn a hammer 20 times over for a hammer each time. Make sure to approach them and smack them with said hammer for it to count.
On 2 occasions I spawned 2 hammers, so made it a little bit quicker. I am not sure what requirements are necessary for that to happen, but it's a quick an easy achievement to knock out.