Withercrown overwrites all previous effects that set the enchanted creature’s power to specific a value. Other effects that set its base power to specific values that start to apply after Withercrown becomes attached to the creature will overwrite this effect.

Any effects that modify the enchanted creature’s power without setting it to a specific value will apply after its base power is set, regardless of the order in which those effects were created. The same is true of counters that modify its power.