Buy Grit or Olaf at the store.

Complete all campaign levels to unlock Nell at the store.

Find one of the Black Hole Army maps. Finish the missions that the map gives you. You will be able to build Neo-tanks with that country.

Complete all Yellow Comet campaign levels to unlock Sonja at the store.

Complete all Green Earth campaign levels to unlock Drake at the store.

Complete campaign mode with an "S" rank on either normal or hard campaign mode to unlock the Sound Test at the store.

Buy Kanbei or Sonja at the store.

Complete all Black Hole campaign levels to unlock Lash at the store.

In the Flak Attack level, capture the city that is located about two squares above your headquarters.

Complete all Black Hole campaign levels to unlock Adder at the store.

Complete all Blue Moon campaign levels to unlock Olaf at the store.

In the Inking Feeling level, the secret map is found in the city in the southern-most city on the Western Isle. You must capture the city in order to get the map.

To unlock Olaf, Grit and Colin, beat the final Blue Moon battle. Colin will appear after buying Olaf and Grit. To unlock Kanbei, Sonja and Sensei, beat the final Yellow Comet battle. Sensei will appear after buying Kanbei and Sonja.

Complete all the hard mode campaign levels to unlock Hachi at the store or buy everything in his store.

Complete all Black Hole campaign levels to unlock Hawke at the store.

In the Show Stopper level, the secret map can be found in the southwestern most neutral city. You must capture the city in order to get the map.

Complete all Yellow Comet campaign levels to unlock Kanbei at the store.

Complete all Green Earth campaign levels to unlock Eagle at the store.

Complete campaign mode with an average "A" rank or get an average of an "S" rank on either normal or hard campaign mode.

Complete all Blue Moon campaign levels to unlock Grit at the store.