Glitch: pause resets attack timer, but some units attack as soon as you unpause. at the third stage, buy tons of musketeers and quickly press space (pause and unpause) whenever they are in attack range. easy win in any difficulty. moreover, the clubman attacks slightly faster then the dinosaur rider, so you can pause just after the clubman hits and then unpause and so on. when the enemy is under your turrent's range (which should be most of the time), you can rapidly pause and unpause with one unit blocking your enemy's way, and the turrent's attack timer won't reset, resulting in you killing all the enemy units in the turrent's range without losing and health or units.
P.S. before you press the "thumbs up" button beaware, this glitch might get fixed if this comment is one of the highest rated comments XP
u can use space (pause) to kill 3 dinosaurs with only 1 club man and any turrent because after hitting space again the animation of their attack is restarted but the animation of the turrent isn't...
u can also use this to train units while pausing and to shoot faster with the war machines (in the future) without being hit by the enemy units.