9. Double Dragon
In its original glory days as an arcade machine, you could blow through an ungodly amount of change trying to finish Double Dragon. Much like many similar games, it was devilishly hard in order to make you die as much as possible, so as to get as much of your money as possible.
That is, until people found a way to save their hard-earned cash. Because, while the enemy AI was well-designed, it had one fatal flaw. Enemies would try and dodge your fiery fists by approaching when your back was turned, often backing off if you faced them directly.
The trick to this is that a move you could do - the infamous elbow strike - that would strike backwards. Gain an awareness of the AI's movement patterns, and you could literally beat every henchman in the game.
That said, you'd still have to face big boss Machine Gun Willy, who can't be beaten with this sweet trick.