https://marco.org/2007/03/25/ok-im-getting-better-at-desktop-tower-defense
OK, I’m getting better at Desktop Tower Defense. The key is to spend whatever it takes to upgrade a few key buildings all the way. The fully-upgraded Squirt Towers cost a ton of money, but a few of them can fend off even the largest army. The fully-upgraded Pellet Towers fire more slowly, but are much cheaper, so they’re good against super-strong bosses.