YMMV: Bubble Tanks

  • Demonic Spiders: Heavy Killers. Like their name suggests, they're very fast and are equipped with machine guns that screw up large characters. Also they'll always be in at least pairs.
  • Game Breaker: With the "improved sell-back" and "cheaper Ghost Towers" upgrades in Tower Defence 2, you can actually profit by building and selling tier one ghost towers. Admittedly it takes ten iterations to afford a single basic tower, but since the game won't start until you let it, with a lot of patience and mashing the 2 and S hotkeys, you can garner a substantial early advantage.