I think you are slightly confused, Hailcomet.
- Decrease Attack reduces the Damage the CB does to your team
This helps your team live longer
- Decrease Defense reduces the Defense of the CB.
This helps your team hit the Boss for bigger hits which helps you do more damage.
- Weaken increases the damage the CB receives from your team.
This helps your team hit the Boss for bigger hits which helps you do more damage.
In a perfect world, you want a Clan Boss team which can do all 3 of the above debuffs.
The goal is to help your team live longer & do more total damage.
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In response to your impression:
You always want all 3 Debuffs.
However, sometimes, you can't get all 3 Debuffs due to lack of hero option's.
For the above reason, Players created a priority list.
The Priority list was designed to help players pick certain Debuffs when they are not able to have all the debuffs on their team.
Number 1 = Decrease Attack
No matter the mode - You always the Clan Boss to hit you softer.
Number 2 = Poison
No matter the mode - You always want Damage Over Time alongside Pyschical Damage
Number 3 = Is Tricky
Players didn't know if Decrease Defense or Weaken is better.
Again in perfect world, You want both.
Sometimes, you don't have hero space to fit in a hero which lets your team do both
This in turn causes a situation where your forced to pick between one or the other.
Players then began doing test to find out which Debuff to use if you can't use both.
The following information was discovered:
- Weaken is better from Easy Mode CB to Brutal Mode because the CB total Defense isn't extremely high.
Through various CB Battles & Tested runs, Players concluded their team did more overall damage with Weaken over Decrease Defense at this point.
- Decrease Defense is better from NM to UNM Mode because the CB total Defense is extremely high.
Through various CB Battles & Tested runs, Players concluded their team did more overall damage with Decrease Defense over Weaken at this time.