Talents are passive abilities for Heroes. The higher the level of a Talent is, the stronger are the effects. The level of a Talent can't be increased, instead the player is given the possibility to roll for a new Talent.
Re-roll means to receive a randomly generated Talent (this means you can even get the same Talent again or with a higher/lower level) at the cost of 300 Gems in the Heroes Altar. The player can either accept the new Talent or forfeit it and keep the old Talent. Both level and type of the Talent are random and don't depend on anything.
Every Hero can have any Talent
Each hero only benefits from his own Talent. Stat boosts (e.g. from Sprint, Berserk, War God) are not shown in the Hero Window, but they do work.
Some of the Talents are less common (Deadly Strike, Berserk, War God) and are generated less often.
Life Drain, Enlighten and Bulwark were Talents introduced in 1.2.31
Increases and reductions multiply together. A 25% increase multiplies the value by 1.25 and a 25% reduction multiplies the value by 0.75. Talents, Skills and Spells that affect the same value are multiplied together.
For example, a hero with War God (15% at 2/5) who is affected by Are's Frenzy (30% at 2/5) and the Druidic Energetic Skill (20% at 2/9) would do 1.15 x 1.3 x 1.2 = 1.8 times or 80% more damage, not 65% more damage. Damage reduction is also multiplied which makes it less effective when combined, for example a Paladin with Stone Skin (25% at 5/5) and Divine Shield (75% at 6/9) will take 0.25 * 0.75 = 0.19 damage which is 81% damage reduction, not 100% damage reduction.
A Cupid, Pumpkin Duke and Druid with 4/9 skill each will increase attack of all heroes by 95% when working together and by 153% when they all have 7/9 skill.
A level 6 Hero Trial wave of 18 Cupids, assuming they all have 7/9 skill at level 130, will increase each other's attack by a total of 42588% if they all use Cupid's Arrow together. And they have nothing on Pumpkin Duke.
The number listed by the swinging sword in the Hero Altar is the time it takes to make an attack. For most heroes, the attack time is 1000. Slow attackers, like Paladin, have a higher number. Fast attackers, like Ninja, have a lower number. When attack speed is increased, the attack rate is divided by the increase amount.
The Ninja, with a base attack time of 800, is as fast as a regular hero with 25% Berserk, making 5 attacks every 4 seconds. Attacks are 1.25 times as frequent with 25% Berserk, so the attack time is 1000/1.25 = 800.
Damage deflection reduces the damage taken by the defender and inflicts that damage on the attacker. Does not inflict damage on buildings. Affects damage but not other effects of skills and talents such as coma.
Flame Guard is better than Blade Shell on average, but Blade Shell may occasionally stop a death blow or slay a weakened attacker.
In terms of damage reduction, Stone Skin is better than Tenacity at level 5 and equal at level 4. Druid or Angel healing benefits Stone Skin more, while Restoration healing is equally effective for either. Stone Skin may hinder the Grizzly Reaper and Succubus skills.
Stone Skin is better than Scorch on average, especially at higher levels, but Scorch may occasionally stop a death blow. Stone Skin may be better than Flame Guard above level 3, but Flame Guard deflects more damage at lower levels than Stone Skin reduces.
Revive is the most useful form of damage reduction even though it only works once per battle. It forces attackers to choose a new target. If the hero does not die a second time there is no need for revival after the battle. It is still as effective as Tenacity against armies.
The Paladin and Marauder damage reduction skills are multiplied with the effect of damage reduction talents, not added to them. For example, a Paladin with 60% damage reduction skill and 20% damage reduction or deflection talent would take 32% of damage, not 20% of damage.
Has a 10% chance to inflict Coma for X sec on target when attacking.
A stunned boss can't harm anyone. This is a very good talent that helps you to fight the boss for full 3 minutes.
Gain X% Energy at the start of battle.
Very good for the proc and run strategy, or to time the skills of your heroes better.
Has a 10% chance to deal Xx more damage when attacking.
This talent can increase your damage by a very good amount, no matter which strategy you use.
Reduces target's Energy by X when attacking.
The boss does most of his damage with his skill, if you can avoid him using his skill, you can even fight for full 3 minutes because his damage output is reduced by a very good amount this way. Ineffective unless most of the heroes on your team have this talent.
Increases ATK SPD by X%.
Reduces the time between skill use, which is very good for heroes with coma and buff. On the downside this fills the boss energy bar slightly faster, so the boss will be able to use his skill more often.
Revive with X% HP restored.
This talent lets you take more hits, works like a health buff in the fight. Boss attacks and fills up the energy bar of your hero, so this can have the same effect as mid level revitalize for the first hero placed.