Percentage-based modifiers

Percentage-based modifiers are a flexible and balanced alternative to numeric modifiers. A usefulness of such modifiers makes them viable at most parts of the game.
example:
10% damage reduction vs -10 damage reduction.
the former is useful everywhere, but the latter is more powerful on only narrow situations where 10% of damage is lower than 10.

Variations:
A.percent depends on player level: 1/20 of player level as percent(or +1% per every N levels of character). modifier "grows with the character".
B.percent depends on chance within specific range: reduce 20-40% of damage(chosen randomly each hit).
C.percent varies depending on ingame time cycle,weather,player health,density of monsters or any external variable:e.g. Maximum at midnight, minimum at midday.
The bound variable/stat synergy enriches gameplay.
D.percent depends on charging/repairing the item/skill granting the modifier:e.g. 100% charge =20$ reduction effect.
E,percent depletes and replenishes after each hit:each hit reduces percent by 0.5 points and each 10 seconds of rest increase it by 0.5 points, upto maximum value of item/skill.
F.percent decays slowly without recovery;20% decays by 0.1% for each hit.
G.percent slowly rises until used and then resets to minimum: 10% rising to max 75%, each 10 seconds of rest increase it by 0.1 points. (used by spell damage and buff modifiers of rare-use skills)