Killing the octopus is actualy VERY easy. Once you got rid of all the enemies, you contrate your armys at the top tower (the one more to the north) and use them to kill the top tentacle. Than you do the same thing to kill the second tentacle. Now you can use all your units brom the north part of the map and go straight to his head. It will take you less than 5 minutos to do that.
Nice game... Cute warriors and simple strategy: go all crazy taking buildings as fast as possible. Dont worry about the cristal thingies, and take the buildings capable of making more units. Do that and its really easy.