Rocket Riot

This might require some grinding depending on how much of the environment you destroy while playing through the story. If you need to go back for this one, pick any level and grab the big rocket power up and start shooting the environment. No need to worry if you destroy it all because it rebuilds itself over time.

This is another achievement you will likely need to grind after completing the required campaigns. This one should come naturally without trying too much along the way to grinding 5000 kills. It really helps your total to go crazy destroying the level with the Gigantic Rocket power-up any time your get one. These have huge explosive power and can obliterate the entire level's blocks in a few shots. 

You can check your progress towards 1.000.000 blocks upon completion of any level in the statistics screen.