How to change damage dealt?

Plugins Plugin Development
1

Eg)

  1. Amplify a player’s attack damage by X%
  2. Reduce fall damage by Y%.

Side note: would this be the most efficient way to “revert” the 1.9 combat update? As in eliminating the swing delay by manually setting the damage of every melee hit to pre-1.9 damage.

2

You can set the damage taken from a attack or anything using

DamageEntityEvent.setBaseDamage(double);

https://jd.spongepowered.org/7.2.0/org/spongepowered/api/event/entity/DamageEntityEvent.html