If a flash game cannot handle that much clicks, don't design games that requires constant tapping of a key to work, like the need to tap space to knock off the alpha zombie, it just freeze everything.
that flash glitch is pretty rare and almost none existent if you follow the guide(no extra tabs/programs running/repeater settings if need be too/cpu affinity if lagging blah blah been repeated a lot) but it is annoying when it does pop up. Pausing and letting flash catch up can save you from crashing sometimes. I'd rather get the game out then outright cancel it because of a small random bug from flash limitations. but oh well.
Spam your units in a single file at the upper edge of the battlefield, do not spread them. Use bombs to slow the enemy down. Your units can do all the damage needed for victory before any enemy can reach you endzone.
The "finished in xx seconds" thing does not belong to this sort of games. Makes no sense at all. You just replay again and again after you have solve the puzzle.
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what mode are you in? the enemies on "The Slayer" Mode is *.25 hp lesser than "The Fool" Difficulty.