KRV is different. There really are OP and weak towers.
You can win every level in the main campaign on Impossible, no lives lost, using just three towers, without even bothering to familiarise yourself with the levels first. (I used Asra and Hellion Tridents, playing on mobile – doubt it matters though.) And don't think that this is about in-app purchases; two of the three towers are free.
Fortunately, the Subaquatic Menace and Frozen Nightmare campaigns provide counters to two of the Big 3 towers which forces a more diverse strategy. It would have been disappointing otherwise.
Cost Efficiency
The most important raw stat for a tower is its cost efficiency. That is, the gold it costs divided by its DPS (damage delivered per second). The lower the number, the better.
Other things matter too: Does it deal damage to multiple enemies and with what footprint? What's its range? What's its fire-rate (the faster the better for the same cost efficiency, to avoid wasting damage on overkill)? Does it stall/tank/stun/slow? How good are its special abilities? Is it still useful when disabled? Can it store attack damage? But cost-efficiency is the place to start.
So let's rank the Level IV towers by cost efficiency. The list assumes that the tower is continuously active and that any barracks units are alive and fighting. Area damage is treated as damage to a single enemy. It is assumed that you have all soul upgrades:
- 1) Elite Harassers: 9.7 (Barracks; 8.6 in melee)
2) Deep Devil's Reef: 10.2 (Mage; includes ranged redspines; 14.7 for magical damage only)
3) Bone Flingers: 11.5 (Ranged; improves to 11.1 with Got Milk III)
4) Wicked Sisters: 12.8 (Mage; improves to 11.1 when set to poison)
5) Infernal Mage: 14.0 (Mage)
6) Spectres Mausoleum: 14.3 (Mage)
7) Shadow Archers: 15.1 (Ranged)
8) Orc Warriors Den: 15.8? (Barracks; assumes attack rate of 1 per sec?)
9) Blazing Gem: 16.6 (Mage; for an attack lasting <1.25 sec)
- 0-2.5 sec average is 11.0
- 0-3.75 sec average is 8.3
- 0-inf average is 5.5
10) Goblirangs: 16.8 (Ranged)
11) Orc Shaman: 16.8 (Mage)
12) Goblin War Zeppelin: 17.8 (Artillery)
13) Grim Cemetery: 18.0? (Barracks; assumes 5 active and attack rate of 1 per sec?)
14) Dark Knights: 23.1 (Barracks)
15) Rocket Riders: 33.1 (Artillery)
16) Rotten Forest: 53.6 (Artillery)
17) Melting Furnace: 68.0 (Artillery)
Ignore the fact that the numbers for artillery towers are terrible. Of course they are, as the whole point of them is that they are dealing damage to multiple enemies. Similarly, most (but not all!) barracks towers exist mainly to stall and tank, so you would expect them to deal less damage than ranged and mage towers.
THE BIG THREE
My big three towers include two in the top three of this list, and one that comes a lot later....
1) Elite Harassers
If you treat them as a pure barracks tower, you will be disappointed by how easily they die. So don't treat them like that. Treat them like a hybrid between a ranged tower and a barracks tower that provides the best last line of defence. Usually, it is a good idea to spam this tower near the back of your defence.
Their cost-efficiency is incredible. Even if the units spend a third of the time dead, they will do more damage over time than, say, Shadow Archers placed at the same point. For this reason, it is okay to place them further forward, e.g. within range of an artillery tower, a Goblirang, or a Blazing Gem with Unstable Power. Plus, their movable rally point gives them a greater effective range than any other tower in the game except Wicked Sisters.
And don't forget that, on top of all of these advantages, they can also stall enemies for a while, usually long enough to get the kill. A ranged tower that you put at the back won't be able to do that.
Upgrades: None of the upgrades are priorities, but get Arrow Storm first if at the back. Get Backstab first if further forward. I never get Fury of the Twilight.
When not to use them? The area damage of Anurian chasers will quickly kill them. More generally, Subaquatic Menace has heavily armoured enemies, and it has enemies that deal a lot of ranged or area damage, against which the dodge ability of Elite Harassers is useless. So in this campaign, they should be replaced by the Deep Devil's Reef, which is a true hybrid between a mage tower and a barracks tower. The Deep Devil's Reef deals slightly less damage and it has a much worse effective range, but it is better against armoured enemies, and it keeps dealing damage after the units die.
2) Blazing Gem
This tower is not as good as its hype. It is better. Provided it spends more than 3 seconds on each enemy, on average, it has an even better cost-efficiency than the Elite Harrassers. With a very long term cost-efficiency of under 6, it makes giant enemies and bosses seem pathetically weak. This will surprise nobody. More controversially, it is also a decent crowd-control tower, at least when compared to other mage towers....
Consider Pond of the Sage, which would be KRV's toughest level without this tower: If you start by spamming Level 1 Blazing Gems at the front and Deep Devil's Reefs right at the back, you will find this level surprisingly easy on Impossible (Asra; Hellion Tridents; mobile; I also build one Rotten Forest in the obvious place). The Blazing Gems are effective against hoards of Anurian Chasers because they are Level 1, so they continuously fire for several seconds to get the kill, and also because they have a fast fire-rate, so suffer less than other mage towers from overkill. Later on, you can upgrade and get Unstable Power, which is very effective for area damage if supported by barracks.
Upgrades: I usually get Unstable Power first, but might prefer Gem of Amplification if I know a batch of giant enemies are coming. I only get Destructo-Ray if I'm running out of ways to spend my gold.
When not to use them? On levels with frozen hearts. They will kill the frozen heart but ignore the resulting frozen soul in favour of a less advanced enemy. The frozen soul will either turn into a full-health frozen heart, or it will escape. I recommend Spectre's Mausoleums instead, right at the back, in Frozen Nightmare. The other four towers might be Elite Harassers, Bone Flingers, Goblirangs and Melting Furnaces.
Blazing Gems are also weak against leap dragons, because they lose focus on every switch between flying and walking. Nevertheless, they are the best mage tower on levels containing leap dragons because their sustained attacks are powerful enough to be somewhat effective even against magic resistant enemies like ice witches and svell druids.
Don't put them right at the back. You want towers placed there to target the enemy that is closest to the exit.
EDIT: I don't use them in Cursed Bargain. See my comment below.
3) Bone Flingers
If Elite Harassers get you physical damage at the back, you need something to get you physical damage at the front. You need Bone Flingers. They have a great cost-efficiency, and their random targeting is an advantage because it gets around the meat shields of enemies that have ranged attacks or summoning powers. Their weakness is their poor range, but good tower placement can deal with that.
Upgrades: Got Milk is a continuation of the basic upgrades, which actually improves the cost-efficiency. That's another advantage: because there are 6, rather than 3, upgrades to get to full power, you can get a high DPS tower without ever spending more than 180 gold on a single upgrade, so you are never forced to save up lots of gold.
The other two upgrades are decent, but because I put Bone Flingers near the front, I only usually get them if I want to spread out my units as a way of dealing with Magnus Spellbane or Arkuz.
When not to use them? I would always have them available unless I'm trying to give myself a challenge. In some Subaquatic Menace stages, I might not build any because Blazing Gems are so effective, even getting by against the magic-resistant enemies. More generally, Goblirangs are often better at choke points for their damage to multiple enemies. Also, don't build Bone Flingers at the back because of their random targeting. You should be spamming Elite Harassers there anyway.
EDIT: Don't use them in Cursed Bargain. See my comment below.