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I just purchased this game for my grand kids. The game appears to me to be totally "pointless"! What do you do? It seems there is no control over and above putting a cannon on the ground to slow-down the "bad-guys". You only get to place a mini robot every so many seconds. And the other two "good-guys" are available all the time!?!!??! What am I not understanding??? The grand-kids love it, but want help!!! I am totally lost in giving them "pointers"!! Help.................!