To begin I'm going to list what can be modified by Modules and what they do and how the modules Interact with them

Stat Name - Positive Effect / Negative EffectGeneral Description
• Cooldown - "-X%" Reduces the time / "+X%" Increases the time
  Generally takes place after the start of an ability but some (Sharen's Invisibility) begin after the ability is finished. This is how long before you can use the ability again.
  
  
• Duration - "+X%" Increases the time / "-X%" Reduces the time
  Length of effect after trigger. Some abilities have multiple duration within them, but all are governed by mods.
  
  
• Range "+X%" Increases the Range / "-X%" Reduces the Range
  The area or distance an ability can effect. Will appear as "m" and mods will effect it manipulatively.
  
  
• MP Cost - "-X%" Reduces the cost / "+X%" Increases the cost
  Cost of the skill to activate or channel.
  
  
• Skill Power- "+X%" Increases power of the equipped Reactor / "-X%" Reduces power of the equipped Reactor
  Mods with "Skill Power" effects the base strength of abilities by increasing the Reactor's Skill Power stat to each ability.
  
  
• Skill Power Modifier "+X%" Increases the power of the Skill Modifier/ "-X%" Reduces the power of the Skill Modifier
  Mods with "Skill Power Modifier" effects scaling of Skills themselves. This will appear as Skill Power +XXXX%. where +X% from mods will be additive
  

In here I'm going to be talking about how the mods work and what should be considered when modding. I'm going to break down this part into 4 parts: Up-time(Cooldown vs Duration), Efficiency(Skill Cost/MP Max and Duration), Effectiveness(Skill Power + Modifier and Range)

Up-Time Here will be defined as how often can you use the ability vs how long the ability lasts.
This is pretty simple and straight forward there's not much really dive deep into.
To start there is two types of cooldowns. Those that begin on the ability cast and those that begin on ability finish.
On Ability Cast
These are the ones that you can get a positive Up-time. I'm Going to use Enzo's 4th as my example because i find it the most satisfying to hit Up-Time Neutral. Enzo's 4th starts off with a pretty awful up-time: 90s cooldown with 7.5 Duration at max level. This gives us an 82.5 second wait between cast. To get positive up time here is just throwing off any mods that give Positive of both. (Multi-talented best frand). My enzo is at 28s(10.2s) cooldown and 10.2s Duration. Simple, but I want to talk about things to consider.
So cooldown's are able to be reduced far more potently than Duration. This is something important to look at. Notice in my Enzo example I went from 90s to 28s without Multi-talented, and 10.2 with multi-talented. However, I only got my duration to 10.2s. Overall the game more % attached to cooldowns than it does for Duration. Multi-Talented for example gives -20% cooldown while it only giving +6% Duration
When considering up-time management cooldown is the easiest to modify and duration the hardest. I did not mention abilities that have no duration. These will only have up-time effected by cooldown.

Efficiency is going to be the ratio of Skill cost and MP Max as well as I will throw in some explanation of Duration's influence.
Skill Cost does not have many high %'s to reduce but each one is extremely effective. Skill cost not only increase the effectiveness of + MP Max, but also reduces the effects of -MP Max mods. It also makes mana orbs and effects like MP in combat/MP out of combat more effective. Costing less MP means needing less MP. Making mods like whats in the thumbnail "Skill Simplification" which gives 84.5% Skill Power Modifier and Max MP -25% a lot more valuable.
Duration increases your efficiency by which allows you to cast less and get more use out of what was spent. IE. 10s duration- MP Cost: 10. This equates to 1 MP/s. Increase the duration to 11s now your looking at .9 MP/S. 10% more efficient and also increasing your up-time by 10%

This is where things get more chaotic. As mentioned before mods with "Skill Power +x%" effects the BASE value given by your Reactor and "Skill Power Modifier +x%" effects the modifying stat given to abilities. Modifier is always additive to modifier. (200%+50%=250%) stat.

• Skill Power x Modifier = Output
  
• Skill Power == Value showed on Reactors + Skill Power %
  
• Modifier == Modifier given to abilities.

If you look at the image above Enzo's 4th has 15% modifier. This means he gets 15% of modifier to start.
Example: Skill Power = 1000

• Skill Power x 15.9 = 159

Example: Skill power + Skill power 50% = 1500

• Skill Power x 15.9 = 238.5

Example: Skill Power = 1000 Skill Modifier + 50%

• Skill Power x 65.9 = 659

When working with a skill that has a low base Modifier there is a massively larger growth in Skill Modifier. 50% Skill power doesn't translate directly to 50% but comes out to be 49.68%. However, +50% Skill Power Modifier translates to something like 314% more output.

Changing the example to a large base Modifier: Viessa 4th

Example: Skill Power = 1000

• Skill Power x 1435.2 = 1,435,000

Example: Skill power + Skill power 50% = 1500

• Skill Power x 1435.2 = 2,152,800

Example: Skill Power = 1000 Skill Modifier + 50%

• Skill Power x 1485.2 = 1,485,200

Now in these examples it is shown that Adding 50% Skill power now does translate to a 50% increase where as adding +50% Modifier only translate to a 3% damage growth.

Range is going to increase your Effectiveness by increasing how many targets can be hit. Buffs mean less chance of Missing an ally when they are far away and dps skills mean in general large counts of targets can be hit.

Mechanically range is not working. Each ability is supposed to have a cap but that cap does not work.

Base range is 100% adding range is additive to this value with 200% beeing max for modding

• 100 + 0 = 100 2m x range = 2m
  
• 100 + 50 = 150 2m x Range = 3m
  
• 100 + 200 = 300 2 mx Range = 6m

Arche Acceleration
Skill Speed and Range increase Modifier effects projectiles and their flight speed and distance.

Survival Traits.
Reactors and their effects on modding
Element mod and Skill type mod effects and explanation.