Friday, January 2, 2009

Tower Defense

In the process of doing research for this blog post, I got sidetracked... for a long time. If you don't know, Tower Defense is a new genre of game where you erect towers that shoot at groups of enemies. The enemies walk, fly, ride, or sail from one end of the map to another, and your objective is to prevent them from getting there.

Apparently the original tower defense game, aptly named "Desktop Tower Defense," is a flash game that can be played in any computer's web browser at Until about thirty minutes ago, I hadn't played this version at all. But through my iPod Touch I've become quite familiar with its successors/homages. Here are three iPhone/iPod Touch games that have really been stealing so much of my free time over the break.

First, Tap Defense. Tap Defense has become very popular and is very accessible because of its price. Yup, it's totally free for iPhone/iPod Touch users. There is a set path that leads from Hell to the gates of Heaven, and you place towers along the path to prevent the monsters of hell from invading. You get 20 lives, and each enemy that enters Heaven takes one life away. The game is over if you lose all 20. There are various enemies, including gremlins, locusts, cerberuses, demons, succubi, firecats, and the Devil himself. Gremlins and cerberi have average amounts of health and speed, whereas firecats are weaker but extremely fast. The Devil, demons, and succubi are very slow but can take a lot of hits. Fortunately, you have different types of towers to counteract these enemy attributes. The standard arrow tower is fast-firing but somewhat weak. Cannon towers have a slower refire rate but do good damage and also affects an area rather than just a single enemy. Water towers shoot water, which is helpful for slowing down faster enemies. Money is earned by killing enemies, and is used to buy or upgrade existing towers, making them faster, stronger, and/or give them longer firing range. You can sell towers you built previously to recoup part of its value if you need the spot or the money back.

The enemy and tower types, as well as the concept of money and upgrading towers is common to just about all tower defense games, but there are some things that make Tap Defense unique. First, halos. You obtain halos by completing certain levels. Halos can be used to "research" new tower types beyond the basic three - once researched, a tower will be permanently available for purchase if you have the money.

Halos can also be used to increase your interest rate - which is another thing unique to Tap Defense. Let me explain. The enemies come in levels, or waves. Once a wave of enemies has gone by and you still have 1 or more lives left, you are shown a "level complete" screen, where you earn bonus money equal to (your current money) x (interest rate). On the easy difficulty level, interest rate starts at 10% so if you end a wave with $90 you get $9 bonus and will start the next level with $99 to spend. This encourages players to conserve money and take extra care to place towers strategically so as to get more bonus cash. If you have an iPhone/iPod Touch I strongly encourage you to try Tap Defense. The price is right.


The next game is Fieldrunners. Fieldrunners is currently $4.99 but they claim the price will go up soon, so grab it now. FR has been very highly touted on the Internets since its release in late November. I was hesitant to spend the money until recently, because at first I didn't know if I'd like the genre, and then after I got Tap Defense I figured Tap Defense would be all I needed. But I decided to take the plunge in a moment of adventurousness and spend-thriftiness. Unlike Tap Defense, which has a set path whose shape is determined by what difficulty level you're playing on, Fieldrunners is more like Desktop Tower Defense in that it's a wide open field and YOU determine what path the enemies take.

How does this work? Well, enemies will walk around your towers in a path that will take them to their goal in the shortest distance possible. So it's up to you to place the towers in the most winding, circuitous arrangement possible so enemies will take longer to get to their destination and to give your towers more time to shoot the enemies down. In FR, the enemies are human soldiers of different sizes that are on foot or on motorcycles, as well as small tanks and flying vehicles. Like in Tap Defense, they have different speeds and strengths and weaknesses. FR has only 4 tower types, as opposed to Tap Defense's 7. The basic machine gun is weak but fast, the goo tower does no damage but slows enemies down, missiles home in on enemies and do high area damage, and the expensive lightning tower does massive damage to a single target. Like in Tap Defense, you spend money to upgrade towers all the way to a max of level 3, which increases firing rate and damage (or slowdown in the case of the goo tower).

Flying enemies totally circumvent your tower "maze" so it's necessary to add some extra goo, missile, or lightning towers along the straight path from the enemy's entrance to their goal. Another thing that makes FR more like Desktop Tower Defense and less like Tap Defense is in between waves, the game does not stop for a Level Complete screen, but instead simply gives you a short countdown to the next wave. However, both FR and Tap Defense allow you to pause the game while you strategize and remove or place more towers.

FR comes with two different maps: a grassy field where the enemies go from left to right, and the "Crossroads" map, where one group of enemies goes from north to south and the other goes from west to east at the same time. This one is tricky because you have to cover both the south and east exits with your towers. This idea of having to use the right combination of tower type and tower location added an extra dimension not present when I was playing Tap Defense. And another neat feature is that you can use the pinching motion that all iPhone/iPod Touch users are familiar with, in order to zoom in on the action.


Finally, there's 7 Cities TD. Like Tap Defense, 7 Cities enemies move along a set path. The premise is that you're in charge of protecting 7 cities, each of which is situated along a river and each of which corresponds to a unique map. The enemies are pirate ships and sea creatures, and your towers line the coastal path leading to a suspiciously Mayan-style temple. Like FR, 7 Cities does not stop in between waves of enemies but gives a countdown to the next wave to let you make upgrades and modify your tower arrangement. Unlike both FR and Tap Defense, however, 7 Cities does not allow you to perform actions while the game is paused, making it a significantly more frantic game.

A unique aspect of 7 Cities is that, like in RPGs, your towers gain experience points from doing damage to enemies. At levels that are multiples of 5, your tower is eligible to be transformed into a modified version of itself: arrow towers can be transformed into "Ballista towers," which are like giant crossbows, and cannon towers can be transformed into trebuchets which cause burning damage. Defeating enemies also rewards you with blue gems, which are used to do normal upgrades to your towers.

One more thing that sets 7 Cities apart from the other two games is its music. It's strictly synthesized midi-quality music, but all things considered it's not bad and it really adds to the atmosphere of the game. So far I have completed 6 of the 7 city maps on easy, but the 7th one seems significantly harder as there are three paths for the enemies to approach along, and thus three paths among which you must divide up your firepower.


I'm not prepared to declare one of them a winner, as each has its own unique gameplay elements. Tap Defense has recently been given five new gameplay modes which adds some replay value to the main game. In "This is Sparta" mode, you start with 3 halos to use as you please, but instead of the normal 20 lives you only get 3. And only 9 towers are allowed on the map at any given time. You may still sell existing towers to make room (and cash) for others. In "Sudden Death," the game is like normal except for your number of lives, and in "Ten Towers" you get only 10 towers while everything else is the same. The "Silver Spoon" mode is exceedingly easy, as you start out with tons of cash and extra halos, and if you can manage to keep your cash reserves up, even a 10% interest rate can make you rich very quickly. Finally, "Credit Crisis" mode gives you $4,000 to start with and that's it... no money from enemies nor from interest. All these new modes are pretty fun, though Silver Spoon is just way too easy.

Fieldrunners has classic and endless modes for both maps. Endless mode needs to be unlocked through completing classic mode once, and differs from classic in that it keeps going past the standard 100 levels until you lose all your lives. 7 Cities also has an endless mode, though I have not given that a try.


These three games have cost me a total of $10, and for all the fun I've had with them, I'd say it's been worth it. If this has interested you at all, please check them out. If you don't have access to an iPhone or iPod Touch, at least check out the Desktop Tower Defense flash game linked above.

Happy new year to all, and Go Bruins!