Raw Damage vs % damage

Units do raw damage each attack. But some gods do also extra Hp% damage : damage based on max Health of the target. To kill the final boss of normal/hard mode, you will need Hp% damage. At lower levels, the boss has too much Health to be killed with only raw damage, so you'll need to do as much Hp% damage as possible. At higher levels, you can use raw damage.

To kill final boss of hell mode, you need damage scaling with shield (Sp%) or insane raw damage output (cannon and eggby are best for shield damage on bosses)

% Damages Buffs, attack speed and Crits

% damages cannot be increased by crits or by increasing damage (for example from ancient blue dragons).
The best buff for % damage is attack speed boost (from witch doctor). This means that you'll do the same % damage per hit, but you'll be hitting more often, allowing you to kill bosses faster.

Note : The only thing that can increase % damage is the Ancien Blue dragon Liberation skill, that multiply damage taken by ennemies, and the golem glove flame that put a mark on ennemies.

% Damages in Hard and Hell mode

Hp% damage is based only on max health. Because of this, enemies that have more shield than they do health will be much harder to kill with Hp% damage, and you'll need more raw damage or Sp% damage as a result.

Example: if an enemy has 10 health, and 1000 shield, 10 Hp% damage would be 1 damage, requiring you to hit them 1010 times overall.

Upgrading Units with Stones

In battle, you can upgrade units using stones to increase their damage - this feature is usually useless, you want to use it only when you're done building and have blue stones to spend.

Abilities increasing attack are based on base damage (white numbers), and damage increases from spending stones do not stack with abilities. For example, a unit with 30k base damage will get +30k damage from a level 1 blue dragon (+100%), and the Blue Dragon buff will not increase as you upgrade it with stones.

Crit Rate

Base crit rate is roughly 15% depending on your relic level. Base crit damage is roughly +100% (also depends on your relic). Extra boss damage is nearly useless.

Buff Units

Support units (witch doctor, ancient blue dragons) apply their bonus to partner too, and bonuses stack additively: if you make 4 lvl 1 witch doctors, both you and partner's units will have their atk speed doubled.

Demon God Upgrades

In-battle demon god upgrade will increase damage of units based on their base damage :
A Clara will get a different attack bonus than a slime.

This upgrade does not depend on unit level; lvl 1 Clara will get the same damage boost as lvl 21 Clara. This boost is usually dramatically bigger than the base damage of unit, but still not that useful nowadays with liberations and Hp% or Sp% damage.

Slow Effect

Slow effects do stack but only for different units: if a tile is covered by 3 different Ice Knights, it is the same is if it were covered by one.
Big Hand's slow from relic however will be add to the slow from Ice Knight. When effects DO stack, they're multiplicative.

Stun Effect

Stunning a stunned enemy will refresh its stun duration.
If an enemy from previous wave is still on the board, he will get 20% chance to ignore stun (meaning attacks that should stun him won't with a 20% chance).
 If he is on board for 2 waves, the chance rises to 40%...
This continues until enemy has 100% chance to resist stun and becomes unstunnable.

Attack Priority

Unless specified otherwise, units will attack the closest enemy. Some units can focus one ennemy until its dead or out of range, while some other will focus bosses.

Multiplicative vs Additive

Multiplicative boosts are much more powerful than additive boosts.

• Additive boosts add together before being applied. For example, if you have two bonuses of +50% damage, they combine into +100% total, giving you 2× damage. Every +50% buff will be the same size.

• Multiplicative boosts apply separately and multiply the result. Two +50% boosts would be 1.5 × 1.5 = 2.25× damage, making them stronger when stacked.

Additive: +50% three times → 1 + 0.5 + 0.5 + 0.5 = 2.5×
Multiplicative: +50% three times→ 1 × 1.5 × 1.5 × 1.5 = 3.375×

For example : if you have two blue dragons their bonus atk will be additive : 100%+100% = +200% attack
But if you have a blue dragon liberation its bonus will stack on top of everything, being multplicative
So if you have 300% total it will be 600% total with the liberation skill

This was the breakdown of the main combat mechanics of CoopTD. But what units should you use? How should you start each game? Check out our Demon God Newbie Tier List, or our Opening Strategy guide, and you'll be clearing difficulties with ease in no time.