There are three skill trees, one for each race: Orcs, Undead, and Demons. While the skill trees are mostly distinct, their structure is all in common.

Each time you gain a level from your experience points, you will be given three skill points, which can be spent on ranks in each skill. Every skill has a prerequisite you must meet before you can spend points on it – most of these prerequisites simply require that you have a certain number of skill points invested in the corresponding skill tree already, but a few require that you have one specific skill.

When you take a rank in a skill, you will get a specific bonus for that skill. In addition, you get a global passive bonus to your firerate, range, or damage for each point you have invested in a given tree.

While some skills are unique to a single tree, there are a few that correspond directly to skills in other trees. Specifically, each skill tree has:

  • A Spell Study skill, which reduces the cost of that tree`s corresponding spell.
  • A Spell Mastery skill, which increases the effect of that tree`s corresponding spell.
  • A Leader skill, which increases the experience gained and decreases the upgrade costs of that tree`s corresponding towers.
  • An Elemental Mastery skill, which gives all of that tree`s corresponding tower the ability to inflict a specific new status effect.




The Orcish skill tree focuses primarily on making money. Every point you spend on an Orcish skill boosts the firerate of all your towers by 1%.



Gold Vault
Prerequisites: None
Ranks: 5
Effect: Increases your starting gold for each level.

Gold vault is fairly useful, since it allows you to start off with more gold for building your initial complement of towers. Mostly, however, it’s useful for being the entry-level Orcish skill, and your key to gaining some of the more powerful skills further down the road.



Height Advantage
Prerequisite: 2 Total Ranks in Orcish Skills
Ranks: 5
Effect: Increases the damage done by towers on high ground.

Not the most noticeable ability, but given the strategic importance of high ground it can be surprisingly useful.



Mining
Prerequisite: 1 Rank in Height Advantage
Ranks: 1
Effect: Gives you an extra starting gem.

Mining is a valuable early Orcish skill that can be a life-saver on levels you find particularly difficult. While its usefulness falls as your overall power level rises, it’s certainly worth looking at if you’re having significant trouble defending your gems.



Cut Down Study
Prerequisite: 4 Total Ranks in Orcish Skills
Ranks: 5
Effect: Decreases the mana cost of Cut Out.

It... lets you cast Cut Out more. Normally this would be completely useless, but it also just happens to go well with...



Cut Down Mastery
Prerequisite: 1 Rank in Cut Down Study
Ranks: 4
Effect: Gives you gold every time you cast Cut Out.

Alright! Now we’re cooking with the beaten, mangled bodies of our enemies! And also trees, presumably. Cut Down Mastery is by far the most powerful skill in the Orcish skill tree – I would go so far as to call it mandatory.

Forests are, essentially, an unlimited resource, save for a very few maps, which means that Cut Down Mastery turns Cut Out into a spell that converts mana into gold. Since gold is approximately six billion times more useful than mana, this turns the relatively esoteric Cut Out into an incredibly useful resource, which will allow you to build masses of towers very quickly.



Marksmanship
Prerequisite: 9 Total Ranks in Orcish Skills
Ranks: 5
Effect: Increases the critical hit chance of Orcish Dens.

Critical Strike isn’t that useful an ability to begin with. Give this one a pass, your skill points are better spent elsewhere.



Bounty Hunting
Prerequisite: 12 Total Ranks in Orcish Skills
Ranks: 5
Effect: Increases the gold gained from defeated enemies.

Generally a full investment in Cut Down Study and Mastery should be sufficient for your income, but if you have a lot of experience bonuses you might want to consider Bounty Hunting to give you a little help keeping up.



Warchief
Prerequisite: 15 Total Ranks in Orcish Skills
Ranks: 5
Effect: Decreases the cost of upgrade your Dens and increases the speed at which your Dens gain experience.

Whether to take this depends on how useful you think Dens are. If you think Dens are a useless third wheel that doesn’t do anything better than either a Crypt or a Temple could, you should pass and take something better. If, on the other hand, you think Dens are a valid compliment to the Crypt and Temple with legitimate uses, you should change your mind, pass, and take something better.



Poison Mastery
Prerequisite: 18 Total Ranks in Orcish Skills
Ranks: 5
Effect: Gives all Dens a chance to inflict the Poison Cloud status effect.

Poison Cloud is a genuinely useful status effect, turning the affected into a walking health drain for your enemy and allowing you to slaughter dense clusters of enemies very quickly. It would be worth taking, except:

  1. You can already do Orcish area-of-effect damage with Ballista Dens.
  2. If your enemy is surviving long enough for poison cloud to be an issue, you’re doing it wrong.
  3. You have to take eighteen total ranks in Orcish skills to unlock it. That’s a grand total of nine ranks in Orcish skills that aren’t Cut Down Study or Cut Down Mastery. You have better things to waste your time on.






The Undead skill tree focuses primarily on mana production. Every point you spend on an Undead skill boosts the range of all your towers by 1%.



Mana Stock
Prerequisite: None
Ranks: 5
Effect: Increases your starting mana.

The weakest of the entry level skills – there just isn’t anything to spend your mana on at the start of the level, except maybe a few Cut Outs. Mana Stock presumably exists to try to make the otherwise horribly overpowered Undead skill tree look better balanced.



Mana Pool
Prerequisite: 2 Total Ranks in Undead Skills
Ranks: 5
Effect: Increases your maximum mana.

Still not exactly a glorious new era of overpowered skills, but certainly better than Mana Stock.



Soul Vault
Prerequisite: 1 Rank in Mana Pool
Ranks: 1
Effect: Gives all Crypts 1 additional charge.

I really should not need to tell you that Crypts are the best tower by now. Giving them additional charges can only be a good thing.



Frenzy Study
Prerequisite: 6 Total Ranks in Undead Skills
Ranks: 5
Effect: Lowers the mana cost of Frenzy

Frenzy is one of the more valuable spells, and Frenzy Study means that you’ll be more likely to be able to cast it when you really need it. A worthy investment.



Frenzy Mastery
Prerequisite: 1 Rank in Frenzy Study
Ranks: 4
Effect: Increases the bonus to tower firerate when Frenzy is cast.

Again, Frenzy is fairly useful. Frenzy Mastery is less useful than Frenzy Study – if a regular Frenzy isn’t doing it, it’s unlikely a stronger Frenzy will help much. But there are worse skills.



Mind Control
Prerequisite: 9 Total Ranks in Undead Skills
Ranks: 5
Effect: Increases the chance that your friend the Chilling Crypt will cause Fear.

Look, it’s a chance to make the already horribly overpowered Chilling Crypt even more overpowered. Yes, take this. Take this a thousand times. Or five, since that’s the maximum number of times the games will let you. But take it.



Mana Extraction
Prerequisite: 12 Total Ranks in Undead Skills
Ranks: 5
Effect: Increases your mana generation rate.

Of the mana-generating Undead abilities, this is probably the best. It’s a global boost to your mana generation, which is by far the most efficient way to improve your spell-casting ability.



Lich King
Prerequisite: 15 Total Ranks in Undead Skills
Ranks: 5
Effect: Decreases the cost of upgrade your Crypts and increases the speed at which your Crypts gain experience.

It lets you get Chilling Crypts faster. Take it.



Ice Mastery
Prerequisite: 18 Total Ranks in Undead Skills
Ranks: 5
Effect: Gives all Crypts a chance to inflict the Freeze status effect.

You know, because you know what race really needed a new way to completely stop the enemy dead in their tracks? The totally not already overpowered Undead. Yeah. Ice Mastery allows even your basic, loser, non-Chilling Crypts up to a 25% chance to freeze the enemy solid. Take all the ranks.





The Demonic skill tree focuses primarily on manipulation of the gems themselves. Every point you spend on a Demonic skill boosts the damage of all your towers by 1%.



Basic Training
Prerequisite: None
Ranks: 5
Effect: Increases the speed at which your towers gain experience.

Basic Training is by far the most powerful of the three entry-level skills, as it enables you to upgrade your towers fairly quickly.



Scorched Treasure
Prerequisite: 2 Total Ranks in Demonic Skills
Ranks: 5
Effect: Does damage to the enemy carry the gem.

And now we see that Basic Training was apparently so good because this level doesn’t unlock anything useful. Scorched Treasure is completely useless, managing only to deal a miniscule amount of damage to enemies who will always be either in a crossfire of several towers or too close to the edge of the map for this skill’s pathetic damage. Take only if you need prerequisites.



Adoration
Prerequisite: 1 Rank in Scorched Treasure
Ranks: 1
Effect: Gives you 20 mana whenever you build a Temple.

And if you thought the skills that take Scorched Treasure as a prerequisite were going to be any better, well, guess again. There are far better ways to gain mana that don’t involve wasting a skill point on Scorched Treasure.



Meteor Study
Prerequisite: 6 Total Ranks in Demonic Skills
Ranks: 5
Effect: Reduces the mana cost of Meteor.

These skills really aren’t doing much to endear themselves to us, are they? You should never be casting Meteor. If you do have problems with gem-threatening emergencies that mandate Meteor’s use, this is probably the skill to take to improve it. At the very least, it’s more useful than...



Meteor Mastery
Prerequisite: 1 Rank in Meteor Study
Ranks: 1
Effect: Increases the damage done by Meteor.

Look. Meteor already does 200 damage to an enemy that’s already in the heart of your defences. If a straight-up Meteor isn’t going to kill it, a Mastery-boosted Meteor won’t either.



All-Seeing Eye
Prerequisite: 9 Total Ranks in Demonic Skills
Ranks: 5
Effect: Increases the effects of the Radiance status effect.

Seriously, why are you still here? Have you not gotten that this skill tree is useless yet?

Jokes aside, All-Seeing Eye is actually one of the better Demonic skills, as using Evileye Temples as support for a killzone is actually a valid strategy. If you find yourself using Radiance a lot and not just upgrading to Evileye Temples to keep the continuous beam, consider looking into this. Otherwise, it’s not worth the four wasted skill points.



Return Portal
Prerequisite: 12 Total Ranks in Demonic Skills
Ranks: 5
Effect: Returns gems on the ground to your cave after a period of time.

One of the more useful Demonic skills, this is actually a solid defence against assassins and ninjas, who have a nasty tendency to carry your gems out of the map slowly in multiple waves.

Do remember, however, that it takes at least four wasted skill points to get this far.



Demon Lord
Prerequisite: 15 Total Ranks in Demonic Skills
Ranks: 5
Effect: Decreases the cost of upgrade your Temples and increases the speed at which your Temples gain experience.

If you have so many skill points invested in the mostly worthless Demonic skill tree that you’re even considering using Demon Lord, I’d say go for it. It’s a good skill, giving a boost to a useful tower type. It’s just that it’s so high up in an otherwise worthless skill tree.



Fire Mastery
Prerequisite: 18 Total Ranks in Demonic Skills
Ranks: 5
Effect: Gives all Temples a chance to inflict the Blaze status effect.

By far the worst elemental mastery. Blaze causes damage over time to those enemies you inflict it upon, which is nice, but it can’t nearly match up to the raw power of Freeze and everything it does do, Poison does better. Ignore this unless you’re a loony, or really heavily invested in Demonic skills. Assuming the two are not synonymous.