Stuck on level 21

Answer from: Doc
Level 21 is when they get pretty tough, but the payout is pretty good (I got $73k for getting 3 stars). I went back and made sure I had 3 stars on all of the lower games and only upgraded my swordsmen, mortar, heal and shock spells. I left everyone else alone and dumped all my money on those four things. I wait until the first wave of guards are on me then make a ton of swordsmen at one time. Using the shock spell on top of the ground spikes and claws pauses them for a little bit and allows you and your men to run thru them. I also try to time it so that my guys are not fighting in them. Make sure to turn them off as you go thru, on the next levels your guys can't even make it to the end if they are active. Hope it helps :)