The activated ability overwrites all previous effects that set the target creature's base power and/or toughness to specific values. Other effects that set its base power and/or toughness that start to apply after Creeperhulk's ability resolves will overwrite Creeperhulk's effect.

Effects that modify the target creature's power and/or toughness, such as the effect of Giant Growth or Glorious Anthem, will apply to the creature no matter when they started applying. The same is true for counters that affect the target creature's power and toughness and effects that switch its power and toughness.