Elemental chains.

The Basics:

Every creature has at least one element bound to it at the beggining of the battle, un-upgraded creatures have 1, while upgraded have 2. During the course of battle the creatures who possess only one will gain 2 if they are attacked, which I will explain later.

To even see these chains, you need to have the Elemental Vision skill under Invocation. I suggest you get this Ability asap as it boosts the warlocks' troops damage output greatly, if combined right.

But seeing the elements of creatures doesn't do much by itself, as doing complete chains early game will be tough, in order to do incomplete ones, you need to make the Altar of Elements in your town, which requires a level 1 Mage guild. The description says something in the lines of : Supports the elemental chains ability, and allows to blow unfinished chains for 1/4 of damage. What is a complete or uncomplete chain? I'll explain soon.

The Practice:

So you've got the first 2-4 unit tiers from the castle, the Altar of Elements built, and the Elemental Vision ability. You are ready to lay down and blow up some chains.

Here's how it works, as short as possible : To build up a chain, you need to attack a creature who has the same element(s) of the attacking creature. When you attack, the element of the attacked creature changes or remains the same accordingly to the attacker, but it gains 1 elemental "combo" point. That means that the chain can be blown for the minimal damage if you attack that creature with one of your creatures who have the opposite elements of the current elements of the attacked creature. Remember that the elements of the creatures you attack are dynamic based on what you've attacked them with earlier so think out throughly what are you going to focus and watch for the ATB bar to know exactly what elemental chains you will be able to stack/blow after you land your current attack.

How do you build up and blow chains? An example: Your Shadow Witch is up on the ATB bar. You look at her elements - Air and Earth. The creature you are attacking has 0 chains built on it and has 2 elements associated with it - Earth and Fire. You attack with the witches and the attacked creatures elements changed as follows - Air and Earth 1 chain built up.

The witches and the creatures had one element in common - Earth. As long as they share at least one element, the attacked creature will get 1 chain combo built up and it will change elemental algnment to the elements which are associated with the attacking creature.

So the creature has 1 chain built up on it, with the current elements of Air and Earth. How to blow it up? Simple. Attack it with a creature who is associated with Water and Fire - A Minotaur King, for example. He will deal double damage to it, blowing up the creatures elements, setting the combo counter to 0 and associating the creature to his elements (Fire and Water), considering the creature is still alive. If the creature had 2 chains built up and the minotaur attacked, the damage would have been 3 times stronger, and so on. Note that Attacking a creature who has Water and Fire bound to it with a Earth and Air attacker will result in nothing if the creature has no elemental combos built up on it. The attacked creature will also retain it's current elements.

That was the demonstration of a complete chain blow. Note that you can also blow a complete chain with attacking a creature with one alignment (ie. Fire) with a creature that has the opposite (ie. Water). The problem is that it needs counters apart from the alignment opposites, making it hard to do early game (due to the lack of troops) and impossible to do late game (due to every of your units having 2 elements). But doing the combo I described above yealds the same damage, so, for the most of the time, you will do Complete chains with 2 elements. What makes an incomplete chain? Simply - unupgraded creatures. They only possess one element bound to them initially, so if you attack a target with Earth associated to it with anything but Earth or Earth coupled with another element - nothing will happen. If you attack it with Air/Earth it will gain 1 combo point and the elements will shift to Air/Earth. Now, what is considered blowing up incomplete chains out of this - the act of blowing Air/Earth with only Fire or only Water. The chains will be lowered by 1/4, or by 1/2 if you built the Altar of Primordeal Chaos in your town.

The Rules:

So you now if you didn't know what follows you'd probably be crying out for the devs for giving the warlock such a destructive tool. But fear not, Elemental Chains Brake as soon as the creature reaches it's turn in the ATB bar, meaning that the elements you stacked up remain, but the creature loses all it's combo points. This also means that slowing an attacker or speeding up your troops greatly enhances your probability of building up and blowing chains, and that agains fast creatures you will have a hard time building up chains as they will reset it each time their turn comes up.

Spells. Warlocks aren't just bound to destructive spells via Invocation or Empowered Spells, but also elemental chains, as they posess a single element tied to them, capable of acting as a built up or blow up of chains. Of course, the Chain blow will be uncomplete since you can only apply one element with the spells. Also even though the spell Magic Missle clearly says in it's description it is not elemental based, believe me, it is, as I blown a lot of chains with it. I'd say it's Fire and Air based from what I've tested so far.

Also, launching an attack on a creature who has chains built on it from a position where another creature has died applies it's own elements at a not so clear algorythm to me . Basically, if you can attack a creature with one of your melee attackers, go for a square where there is a corpse of another creature, chances are that you will inflict more damage.

Since this is a warlock ability only, I'll write the elements based around each creature in the town:

Scout: Water
Blood Witch: Air
Minotaur Slave: Fire
Rider: Earth
Deep Hydra: Water
Matron: Earth
Deep Dragon: Fire

With the upgrade, all the creatures retain their original element and gain a new one:

Assassin: Water/Earth
Shadow Witch: Air/Earth
Minotaur King: Fire/Water
Royal Ravager: Earth/Fire
Chaos Hydra: Water/Air
Matriarch: Earth/Air
Black Dragon: Fire/Air

The same pattern is for all the other towns' craetures, they get one element and another one after upgrading, but I feel it's not as needed to post as the warlocks units (and it's a pain to gather)

Translation. Almost literary. I skipped some of the author's lyricism.
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Theory:

Every creature has at least one elemental bond at the beginning of battle: unupgraded - one, upgraded - two. During the battle, creatures that have only one bond will gain a second if they are attacked - explanations follow below.

To see these bonds (bond chains), you must have the Elemental Vision skill under Invocation.

Seeing the elemental bonds of creatures doesn't provide much on its own; constructing complete chains is difficult in the early game, and to construct an incomplete one, you must build the Altar of Elements in your town, which requires a level 1 Mage guild. Description (of the building): supports the ability (to form) elemental chains and the detonation of incomplete chains for 1/4 damage. What a complete and incomplete chain are is explained below.

Practice:

To build a chain, you must attack a creature (A) that has the same elemental bond as the attacker (B). When B attacks, creature A's elemental bond changes or remains the same according to the attacker's bond and gains 1 combo point. This means that the chain can be detonated with minimal damage if creature A is attacked by one of the creatures with an elemental bond opposite to the one A possesses. It must be remembered that the elemental bonds of creatures change depending on what they were attacked with previously, so you must plan your actions and monitor the ATB bar to know exactly which chains can be constructed or detonated.

How can a chain be built and detonated? Example: let's say Shadow Witch takes her turn. Her elements are Air and Earth. The creature she attacks has 0 existing chains, and its elements are Earth and Fire. After the Shadow Witch's attack, the attacked creature's elemental bonds change as follows: Air and Earth and 1 constructed chain. Shadow Witch and this creature have a common elemental bond - Earth. As long as they share at least one element, the attacked creature will receive one combo point in the chain and change its elemental bonds to those of the attacker.

So, the creature has one chain and elemental bonds with Air and Earth. How do you detonate it (the chain)? Simple. It must be attacked by a creature associated with Water and Fire - let's say a Minotaur King. He will deal double damage, detonating the chain, resetting the combo point counter to 0 and changing the creature's elemental bonds to Water and Fire. If the creature had 2 chains, the damage would have tripled, etc. It should be noted that attacking a creature with Water and Fire bonds using a creature associated with Earth and Air will yield nothing if there are no elemental combos on the attacked target. The attacked creature will also retain its own elemental bonds.

This was an example of detonating a complete chain. Note that you can also detonate a complete chain by attacking a creature with only one elemental bond (Fire) using a creature with the opposite bond (Water). The trouble is that this requires separate tracking of opposing elements, which is difficult in the early game (due to lack of troops) and simply impossible at the end (since all units have two elemental bonds). But constructing the combos described above causes the same damage, so throughout almost the entire game, complete chains of 2 elements will be constructed. Who constructs incomplete chains? - Unupgraded creatures. They initially have only one elemental bond, so if you attack a target associated with Earth using someone without an Earth bond or with Earth paired with another element, nothing will happen. If you attack it (the target) with an Air/Earth creature, it will gain 1 combo point and the bonds will change to Air/Earth. And now, what is called detonating an incomplete chain - exploding Air/Earth using only Fire or only Water (note: this isn't very logical - Air usually opposes Earth, so why hit it with Water or Fire to explode? But I translated it as written). Damage from an incomplete (IMHO, that's how it should be understood) chain is 1/4 (of a complete one) or 1/2 if the Altar of Primordeal Chaos is built in the town.

Rules:

Elemental chains are destroyed as soon as the creature's turn comes - the changed elemental bonds remain, but all combo points are lost.

Magic. Warlocks are not only linked to destructive spells via Invocation and Empowered Spells, but also through elemental chains, since they (meaning the spells) are associated with one of the elements and are capable of both constructing and detonating chains. Although the description of the Magic Missile spell clearly states it is not elemental, many chains were successfully detonated using it. Based on tests, it is associated with Fire and Air.

<furthermore something about gaining an advantage by taking a position on a dead creature. In my opinion, the reliability of this (semi)bug's connection to the ability in question is doubtful>

Elemental bonds for underground dwellers:

Scout: Water
Blood Witch: Air
Minotaur Slave: Fire
Rider: Earth
Deep Hydra: Water
Matron: Earth
Deep Dragon: Fire

Assassin: Water/Earth
Shadow Witch: Air/Earth
Minotaur King: Fire/Water
Royal Ravager: Earth/Fire
Chaos Hydra: Water/Air
Matriarch: Earth/Air
Black Dragon: Fire/Air