Note to self: in case of a zombie invasion standard operating procedure is to run down the road like a doodlebug and throw yourself infront of humvees.
The one part that I thought was unfair: there is a root by the barrels. You have no idea what it is but if you put it in the potion, the potion doesn't work. There is no reason not to suppose that the root is as necessary as the mushrooms. In fact the root serves no purpose at all.
In any hostage-taking situation it's important to remember that your bullets will pass harmlessly through the hostages and bystanders while the terrorists bullets will be immediately fatal.
For the final battle, the winged shoes are your best bet - the extra attacks worth it. Also (you probably figured this out) you need the robot as your buddy or your attacks will do no damage.
For level 17 connect the two in the corner to the third one (the one closest to the enemy). Then stretch a line from the third one to the enemy. You must cut and re-attach lines from the two feeder cells before the attack line snaps back. You have to move quickly on this one.
Here's a simple strategy that I used to beat every single battle: don't use any iron, load up on gold mines (dark merchant if you have a couple), and 3 "parting gift". Play "parting gift" as soon as you can then spam peasants, fresh skeletons and other cheap units that don't need iron. As noted elsewhere, the ultimate pack is the one to buy. Portal growth is good for increasing profits.
Two comments on strips:
1) BUG!!! Say you have 20 peasant cards and 5 peasants in one of your decks. If you tear up one of the 20 it will remove the peasant from your deck EVEN THOUGH YOU STILL HAVE 19! In fact it will remove it from every deck that contains a peasant. This is very annoying.
2) Strip pack contains only 1 card so it's hardly ever worth it.
 "Road of the Dead 2"){kind=icon}
 "Don't Escape"){kind=icon}
 "Strike Force Heroes 2"){kind=icon}
 "Monster Legions"){kind=icon}
 "Wrestle Jump"){kind=icon}
 "City Siege 2"){kind=icon}
 "The Legend of the Golden Robot"){kind=icon}
 "Tentacle Wars"){kind=icon}
 "Cardian"){kind=icon}
 "-The Siege Of Theldale-"){kind=icon}