Mass Diminish

Effects that raise or lower a creature's power and/or toughness, such as the effect of Titanic Growth, will apply to that creature no matter when they started to take effect. The same is true for any counters that change its power and/or toughness.

In a multiplayer game, if you leave the game after Mass Diminish resolves but before your next turn begins, its effect lasts until your next turn would have begun. It neither expires immediately nor lasts indefinitely.

Mass Diminish overwrites all previous effects that set a creature's base power and toughness to specific values. Any power- or toughness-setting effects that start to apply after that ability resolves will overwrite this effect.