Author's note: This guide is a supplement to the excellent Aussiedroid's DG Tower Guide

AussieDroid's DG Tower Guide

While excellent, I felt it lacked a certain discussion on the STRATEGY in tower placements and groupings, so this is my attempt at supplementing that knowledge.

I assume that you are familiar with the basic mechanics of the game, how to place tower, how to upgrade tower, and need that extra... something in order to get "no cores lost" and such.

First, how does a defense mission evolve? How does it start and mature?

Tower Placements generally have three reasons:

• You're trying to PREVENT the aliens from walking that way. (Blocking off exits to force a path) i.e. BLOCKERS
  
• You're trying to deal damage to aliens in a specific area (general damage) i.e. KILLERS
  
• You're trying to enhance the damage of a particular tower by pairing it with something (TEMPORAL tower) or get extra resources (i.e. COMMAND tower) i.e. HELPERS

If you can make a tower do more than one purpose above, even better.

While this is probably pretty "bloody obvious" to tower defense players in general, there are certain nuances caused by specific tower strengths and weaknesses that you need to think about.


BLOCKERS

If there are multiple paths through the playing field, your first job should be to block off one section of the playing field by building 2-3 towers at the entrance, just make sure the aliens do have a path, albeit a longer one than before you placed anything.

Don't forget to put shield-poppers early (while using cannon as blocker is expensive, one of them near the entrance is always good).

The idea is to distribute the blocking across the entire path, shaping it to be as long as possible. You can improve the exact path later, but the "macro" or "overall" path shaping needs to be done early.

Any tower can be a blocker. The trick is achieving the same effect with the fewest number of towers, so you leave room for other towers.


KILLERS

The towers that actually do damage should be clustered, with support towers like command and temporal in the middle, concussion, inferno or tesla in the corners, and guns to plug any "gaps". This is discussed in the section on tower clusters.

Inferno or tesla usually goes at the end of a "wall", or the inside of a curve, for maximum coverage of the path. Behind them would be temporal and/or command towers. If there's still room, put cannon behind for handling leakers and/or meteor for some long range fun.

Inferno and Laser generally needs help from Tesla and other shield popping towers to wear down the shields beforey they can achieve full effect. Reserve them for towers that are further in.


HELPERS

Command tower and/or temporal towers belong in the center of a cluster, probably second row because first row would be the shooters, like gun, concussion, inferno, and so on.

You should place the temporal tower to overlap slightly if you can, as this will likely result in maximum slowdown of the aliens. However, this may be difficult to arrange. Usually temporal towers are added as an afterthought. You may need to sell off some towers without compromising the path shaping to get optimum placement for the towers.

You put blockers in the initial "path shaping" phases of defense, with some killers. Helpers should wait until the "local path optimization" phase.

NOTE that some killer towers, such as tesla, work as shield poppers, so they will help laser heat-based towers like inferno and laser, so they are technically both killer and helper towers.

Tower defense is about where to build as much as it is about what to build, and when to build it.

Defending a particular map actually has multipe phases:

• Shaping overall path -- blocking off island entrances to force specific paths among the various islands.
  
• Shaping local path -- adding additional blockers to further optimize the path within the island itself
  
• Optimizing damage output along path -- upgrade and replace towers to maximize damage

You can't spend too many resources shaping the path because you may have enough firepower along the path to kill the aliens, being too "spread out". The trick is to know when to start shaping general path by adding towers to extend them, and when to just add firepower to existing path (i.e. optimizing damage) to kill things.

We'll discuss "timing" the towers later. For now, let's concentrate on the "where".

Shaping Overall Path

One look at the map and you should be able to spot where you need to block off to force the aliens go the long way around. On maps with multiple islands, the path can be very interesting indeed.

Use the minimum number of gun towers to do that job. You can substitute a cannon tower in there if you expect to see some air threats early on. Or even a missile tower if you can afford it.

While shaping the general path is important, the amount of firepower within the path is also important. Gun towers used for blocking are lacking in firepower, and thus they may not kill the aliens, even when the path is optimized. You have to balance between making the path long enough vs. adding enough firepower along the path to kill the aliens.

Generally, if regular aliens (not bosses) are making it to the core, you need to really upgrade firepower along the path. A general rule of thumb is regular aliens should die before they reach the core, and bosses should be severely weakened by the time they reach the core.

Once general path has been shaped, it is time to implement general "clusters" and shape specific paths, which is discussed in the next section: Shield poppers up front, followed by crowd thinners, and finally, generic grinders to handle any leakers.


Shaping Local Path

Generally, each "island" or adjacent small islands would make up one tower cluster. If the island is pretty big (16-20 squares) you can make small rat run maze on each island. And if there are a lot of islands, you may be able to make the aliens run through each island twice

Study each island carefully. Each island should have matching exits and entrances, and no alternates. Some islands with two in and two out can be "bifurcated" (cut in two) with turrets to force the aliens to walk through it twice. This is especially apparently in the final level in Awakening campaign.

The idea is to force the aliens to go through the most squares, but not blocking their path. generally that means a lot of U-turns and "walls" of turrets. However, this phase is often concurrent with the next phase, optimizing damage output along path.


Optimizing Damage Output Along Path

Shaping the path of the aliens is not a quick task, as you usually can't afford to put down more than a few towers at a time, so one must optimize the damage output by placing the towers in the proper order.

The longest range weapons, like meteor, can go anywhere, and thus, would be placed last. And only used as 'fillers'. Though they generally go in the middle for the the maximum coverage.

The shortest range weapons, like inferno and tesla, are almost always left at corners, where they can cover the path most efficiently (i.e. how many squares it is adjacent to). If you put it as the "end of a wall" it can be adjacent to no less than 7 squares out of 8 of the path.

Next best place is as part of one square thick wall, next to the corner, where it is adjacent to 6 out 8 squares of the path. This space is also good for laser towers.

In the middle / 2nd row should go the command tower and temporal tower, to provide maximum coverage for the towers already placed.

Upgrade one tower out of each cluster at a time. You want to space out the upgrades over time as the tower is NOT shooting at enemies while the upgrade is in progress. Upgrade the towers near the path where the enemy crosses multiple times. In general, it's better to create a level 3 tower than 3 level 1 towers, unless you need them for blocking purposes.

Most people approach the level from the entrance(s) and put obstacles between it and the core. This is the WRONG approach.

Instead, work from the core OUTWARD. So you can identify the chokepoints around the core.

Follow each path to the core, back outward, see where it can be blocked with minimum of turrets, and if that leaves to a longer path for the aliens than the other path. Let's take an example. This is "Barrier to Entry" map (original shot is from John P. Wachsmuth's FAQ/Guide), in normal mode:


Come out of the core, you have two paths, marked as "1" and "2" on the map. (1 is the western exit, while 2 is the southern exit) Which one should be use to lure the enemy in, and which one should we block? If you look at the landmass connected to "1", you'll see it's smaller than the landmass connected to "2". The "rat run" you can creat with "2" is going to be longer. The decision should be to block off 1 by placing towers at the X's next to it.

From there, you study how the aliens have to get to you, which entrances and exists, landmass wise if needed, else within the landmass itself, and design the path to take the aliens across the maximum number of towers.

To give another example, here's the final level in the Awakening campaign: Last Stand. This is how it appears in the game (all credit goes to M Haller[www.mhaller.de])

NOTE: this is purely talking about tower placement as "blockers'. WHAT towers to put in is in the next section. The general idea is put in gun towers to block, and throw in an occasional cannon tower as temporary air defense.


Though for better visual organization we'll show it like this (same thing, really)


I've numbered the islands in their LOGICAL order, rather than their visual order.

I'll name all the land bridges by the islands they serve, and if there are two, I'll name them North or South or East or West. B1-2N would be the northern bridge between islands 1 and 2, for example.

Once you see the level this way, with the two entrances, it's immediately obvious that the initial tower placement should route ALL traffic through Island 10. The idea is to create equal length runs from two entrances, with maximum overlap. So the battle start out shaped like this:

Northern entrance: 4 --> 5 --> 10 --> 5 --> 3

Southern entrance: 8 --> 9 --> 10 --> 5 --> 3

Let's call this "Defense Phase 1"



You can shape the northern route by blocking off B4-2E and B4-2W (that's bridge between island 2 and 4 east, and west) and B4-5N (northern bridge between island 4 and 5). Place enough towers on 5 in lower left corner to force the traffic from B4-5S onto B5-10W, so they have to U-turn back up to 5.

You can shape the southern route by blocking off B1-2N and B1-2S with just 3 towers on 2.

I've placed the towers as "X". Your map would look like this:



There's a bit more room on Islands 2 and 3 we can use to enhance the route. Let's call this Defense Phase 2.



We can further shape the alien path by as we've now force all traffic onto 5 on the eastern side. Place towers on 3 to divert the traffic onto 4, then 2, and finally, 3. The tower on 2 is actually optional, but well worth it, being very centrally located.

Northern entrance: 4 --> 5 --> 10 --> 5 --> 4 --> 2 --> 3

Southern entrance: 8 --> 9 --> 10 --> 5 --> 4 --> 2 --> 3

I've placed the towers as "O" on the map, so your map would look something like this:




Now we move onto Defense Phase 3



Here we can be a bit creative, but the idea is to for force the convergence point between northern and southern traffic further up the island chain.

Let's first consider the Southern incursion. (You can analyze either one, doesn't matter, I'm just showing you my thinking process). To mess with the southern incursion it should be forced onto island 6, and they'll automatically go onto 7, then 9 and 10. We can further improve this by adding towers to 6 to force traffic into 1, then 2, back to 1, and have it come back down to 6, where it will flow to 7, 9, and 10. And this can be done incrementally.

These towers are marked by * (asterisk) in the following map.


Now we have to tweak the northern army, as we want it to travel to as many islands as possible before coming back to 10.

The best route seems to be 10, onto 9, up to 7, converge with southern incursion at island 6 or 7, then from there you just route it back to 10, using whatever's available, and you have many options, but the general idea is the same. Use two towers at 10 to force northern incusion onto 9, then 4 towers at 9 to force onto 7. From there you can choose to push the traffic onto 6 (converge with southern incursion) then down to 8 and flow over to 9 then 10, or let 6 come over to 7 and converge into single incursion down to 9 and back to 10.

If you do that, you may end up with something like this:

Now that we have covered WHERE to build, let's discuss WHAT to build. And here I introduce a very obvious idea: Tower Clusters.

Tower Clusters are groups of towers that work together toward a common purpose for maximum efficiency of killing aliens.

In general, tower clusters have three purposes:

• Shield Poppers -- destroy the shield on shielded enemies
  
• Crowd Thinners -- take out a lot of smaller enemies together
  
• Other / Generic Grinders -- just do some damage, lots of damage, to all comers

Shield Poppers

Enemies get shields later, and shields make the enemy almost immune to heat damage. So shield poppers needs to be deployed early, as far from the core and close to the path as possible. Shield poppers should be at the convergence point if there are multiple entrances, with as much rat run you can arrange with blockers. The idea is to pop the shields on ALL aliens long before they get to the core, so the rest of the towers can then hit them.

Tesla tower does 2x damage to shields, and thus is the best shield popper unit. It also has this "stored charge" capability that allows it to save up energy for extra damage if it doesn't see an enemy, but that should not be relied upon as usually enemies come in too fast to allowed much of that stored charge. If possible, use temporal towers to slow the enemy down so tesla tower can take more shots.

Upgrading tesla tower is debatable, as it does not noticeably increase rate of fire. Instead, it allows more stored charge between waves, and thus a bigger "burst" of damage and more "chained" damage. Thus, tesla tower should be deployed in groups, with command and/or temporal between them.

Tesla tower should be a part of the rat run with the enemy unit walking past it at least twice along the path going, and if the path is a round-trip. walk past the tower total of FOUR times, getting zapped multiple times at each passge.

Cannon is good as a backup shield popper. If you put three or four of them all over the map they'll kill the shields of most regular aliens. You want to let each tower take as many shots as possible, using blockers to herd the aliens to maximize # of shots the cannon tower can make. Using temporal towers to slow the enemy down is helpful, but not required as the cannon fires slow enough that this would not help that much.

Cannon has a secondary purpose as anti-air, but that's more of a bonus feature.

Gun tower doesn't make a very good shield popper. It is just too weak. If you have the money, upgrade a cannon tower instead.


Crowd Thinners

Crowd Thinners have one job: to thin out a whole crowd of aliens clustered together with area damage weapons. Concussion is best, but inferno is not a bad substitute (if you pop the shields first). And meteor always helps, albeit a bit slow.

Tesla tower is not suitable as a crowd thinner, because a green (level 1) tower can only "chain" the damage to one other alien (total of 2). If you upgrade to max (level 3) it can chain up to 4 aliens to damage. But that's very expensive. Concussion is more efficent resource-wise.

Crowd Thinners do little or no damage if the enemies are shielded. Thus, they need to be deployed well after the shield poppers, esp. the fire-based towers like infernno, which does very little damage to shielded enemies.

Crowd Thinners should be supplemented by command towers and temporal towers to ensure they get in a lot of hits, as most of the kills will happen here. Upgrade temporal towers to expand its range for maximum coverage . Have some overlap as temporal towers operate in pulses and you really want the pulses to "alternate" or "tick-tock".


Generic Grinders

Generic Grinders are not a specific cluster, but rather, just about anything else you setup that serves to deliver damage to aliens as they run through your "rat run".

Laser towers are good grinders after the shields have been popped. Place there where they can keep the beam on the enemy for as long as possible, and upgrade them to deal more fire damage.

If you have some space left near the center of the field, leave them for meteor towers. They deliever damage all over the place, except next to itself. They are good "filler" towers.


Special Case: Missile Towers

In a lot of maps missile towers are optional, because your regular cannon or gun towers are spread out enough to take down any air threat. However, you may want to buy one missile tower and place it between the core and the air unit entrance, as to give it maximum engagement distance, as sort of "backstop" against any air units that leaked through. Often, air units are timed to arrive when the cannons and guns are engaged with ground units. As missile tower only engage air units, it can't be distracted.