Design: Picking Apart Flash Element TD
I haven't played the original Warcraft III mod on which Flash Element TD is based, but I have put way too much time into playing the flash game. Well, not so much now that I nearly broke 100K. But while the praise may belong more to the fans and developers who created and evolved the gameplay that the flash game was modeled after, I think David Scott's game is a model of simplicity and elegance in game design. And I'm really excited about his new project, "Flash Circle TD" (which he's shown a WIP video below).



So what has made Flash Element TD so popular? Besides the fact that it's free...

I don't think it's not the ripped-off Warcraft III graphics. I believe it's *gasp* pure gameplay. There are a few simple factors that interact together to form an elegance of decision-making. I don't consider myself a very good game designer by any means, but since I have been paid to do work in that capacity before, I'll pretend that I know what I'm talking about.

First of all, the game has a direct contention between long-term and short-term goals. Short term safety is only gained at the expense of long-term gains --- both in points, and in the capacity to provide further safety. The interest gained at the end of each turn - especially with the interest rate upgrades - is not only a huge factor in the final score, but is absolutely critical in surviving the later rounds. Spending all you have to fight off the critters will soon lead you to a point where you can no longer keep up.

To make the delicate balance even more interesting, being overly cautious in favor of the long-term view will not only bring you closer to losing the game, but will also impact your gold, depleting the very resource you were trying to save. Also, if you find that you erred on the side of being too conservative, rushing to remedy the situation later rather than sooner may end up costing more than if you'd done it correctly in the first place.

Each tower and its upgraded versions have three major, differing characteristics: Fire Rate, Damage, and range. They always seem to fire at the furthest-along creep that is within their fire range. With this standard behavior, on a linear track with no overlapping fire zones you could calculate exactly how much damage a tower could do to a line of creeps of given length. You could divide this damage by gold piece cost and probably figure an optimal cost / damage strategy based on that.

But there are some really fun wrinkles that give the game the "Emergent Complexity" Noah Falstein talks about. The biggest is placement. Because the path the AI takes twists and bends around, not all positions are created equal. So the equations to calculate the optimum cost-effectiveness of a tower is much more complex. For the arrow towers, which have increasing ranges as they are upgraded, it's even more complicated, as optimal positioning for a level 1 arrow tower isn't the same as a level 3.

Then there's the issue of two towers with overlapping firezones, and "spillover" when a unit is killed (the extra damage that would have been done just "goes away"), and gaps in the line as critters in the middle of the line get taken out. But wait, there's more!

A huge factor is the special abilities of certain weapons and levels where the critters are immune or resistant to those special abilities. "Splash damage" radius for several weapons acts as a multiplier to their damage when creatures are not spaced far apart. The water tower slows creatures down, allowing other weapons within range to do more damage to a line (especially with splash-damage weapons, as slowed creatures tend to bunch up), but certain levels have creatures immune to their effects. Cannons and air towers have restrictions on what creatures they can hit. And then there's the boss levels, where optimum placement for defeating lines of creatures might be less effective against a single, high-hit-point boss.

The ability to sell off towers - even in mid-level - is another very interesting mechanic that throws a wrench into the works of the best-laid strategies. Because levels contain uniform groups of creatures (something I once thought was a design flaw, but I've changed my mind on it for this very reason), sometimes towers might only be desired for a single level. Once the last critter has passed that tower's range (or possibly even before), it's possible to sell it off for a 75% refund. Interest is only calculated at the end of a level, so if you have your towers places so that you can sell unneeded towers before the last critter dies, you can still use that gold to earn more money.

As to deficiencies, the biggest is a lack of any sort of "save game" option. In order to go back and tinker with your strategy, you have to start over from the beginning. That's a big reason I haven't gone back and tried to break 100,000 points.

You can overlap tower positions, but it's a pain in the interface. Either that ability should have been removed entirely from the game, or made simple to do. Apparently, for the upcoming circle TD, that will no longer be possible.

The interest rate research item is such an overwhelmingly potent factor in final score that there is really no choice in the matter for your first researches. This is too bad, as the other tower types can be interesting choices earlier in the game. The uniform monster types are another factor that discourage selection of certain research items until late in the game (if ever). For example, the levels consisting entirely of "immune" creatures makes the selection of the water tower ineffective until after the last "immune" level. Since you are going to have to be able to take on several levels without them anyway (except for their damage - which is small but rapid and splashing), there's no point in incorporating them into your overall placement strategy.

While it's hardly a deficiency, I can't help wondering what interesting twists a different map layout would have. Though with the limited screen real-estate available for the map, I don't know how much layout variety would be available beyond what's already there.

Ultimately, the thing that fascinates me about Flash Element TD (and all Tower Defense style games, from the limited number I've played) is how the interaction of simple elements can combine to create such compelling gameplay. It gives me something to think about.


(Vaguely) related howlings at a digital moon:
* Designing a Computer RPG Rule System
* How Do You Create "Fun?"
* Free Game: Flash Element Tower Defense
* Mistakes in Game Design

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Labels: Free Games, Game Design

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