- Demonic Spiders:
- Heavy Killers in 2. 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.
- EMP Creeps in Tower Defense 2. They completely disable all towers around them for a short while when killed, that even includes your Mega- and MegaMega- towers which will temporarily destroy your firepower.
- 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.
- The Mega-Tower, which can be made by morphing 4 fully upgraded towers into one, allowing for vast amounts of attack combinations. Even worse is the MegaMega-Tower, which is 4 mega-towers rolled into one. Next thing we know, the 3rd game will allow us to morph 4 MegaMega-Towers into one MegaMegaMega-Tower...
- Goddamned Bats: Dodge Creeps in Tower Defense 2 pretty much cause Character Select Forcing by having a massive chance to Dodge the Bullet, but stuff that aren't bullets (i.e. Shockwaves) will always hit them and they don't have that much health.
YMMV / Bubble Tanks