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As I'm getting into some of the higher levels (albeit on lower difficulties), I notice that sometimes a path that is open is never followed, due to the way enemies spawned in that wave. This led me to question: are the spawns and approach routes deterministic? Knowing this would allow me to never block certain routes, because I'd know enemies would never approach that way. I'd also be able to develop a circuit of tower repairs if I knew enemies always attacked from one direction first, then the opposite - and so on.

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up vote 7 down vote accepted

As far as I've seen for the general case, yes, pathing seems to be generally pre-determined. The only exception that I've seen is when enemies divert to attack players.

In my experience, I've yet to see main paths not be used except when I killed every enemy intent on that path before it could take that path. The thing to note is that the pathing is calculated only to the targets available and generally tries to find the nearest targets to the point of entry. Some enemies will go a little farther if there are multiple targets in range, but I've never seen one cross the entire map to get to a target when another target was nearer. This means that paths between an entry and a target that is quite far does not need the defenses as the enemies won't go that way when there are nearer targets. The problem is that the targets themselves are not always deterministic as in the case of the Christmas level where the targets are selected at random from the pool of targets.

From what I've seen, shields and blockers are not to divert the enemy, but to draw the enemy agro towards them rather than the towers. They act more to delay the enemy, possibly exposing them to more damage, than they do as roadblocks.

I find effective strategies to employ are:

  • Look for choke points and bottlenecks where you can use fewer towers to greater effect.
  • Put towers near entry points to kill enemies early, but out of the enemy path if you can so as to avoid the need to repair. Faster kills = higher score. For DPS builds, you may need to use your towers to draw agro while you navigate the map so this doesn't always work and in these cases and shields and blockers become quite useful for buying time.
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I've adopted this strategy in the past, but I've found that especially skeletons will ignore defenses and head straight for the crystal if I leave a route partially blocked. – agent86 Apr 12 '12 at 13:32
@agent86 I suspect the path of the enemy is determined at the spawn, and since skeletons are often summoned, they have a different path as its calculated from a different point at a map. – l I Apr 12 '12 at 14:21
@agent86 this was very obvious on the glitter map since the mid spawn rarely goes for the top crystal but skeletons and the summoners occasionally head in that direction due to different pathing – l I Apr 12 '12 at 14:22
Thanks for the detailed response skovacs1. It makes more sense as I consider both pathing and targeting. I believe the game even has a tip somewhere about Ogres getting easily distracted, which essentially would mean you can draw them off their path with aggro. Perhaps to yx's point, maybe mobs like skeletons don't have a path at all and their direction is determined entirely by aggro toward players or crystals. – EBongo Apr 12 '12 at 14:25
@agent86 To your original comment, it may still be necessary to block the routes, I guess we'll have to experiment. One tower to block is still different than the layering we typically do. In that round last night I had two traps that never fired the whole round, which also means enemies never even approached the blockade behind them. Perhaps because the path was blocked, perhaps not. – EBongo Apr 12 '12 at 14:27

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