In Avatar The Last Airbender a major point of the plot is Sozin's Comet, which every one hundred years passes close to the planet and greatly enhances the power of Firebending. While there are normal periodic situations when an element might be slightly enhanced (Fire is stronger when the sun is out, Water when the moon is out, etc), are there other rare situations similar to the comet during which the other three elements (Water, Air and Earth) are greatly enhanced?
Thus far, the only other situations shown to increase a bender's ability are:
- The full moon strengthens waterbending. This could arguably fall under the moon simply being out, but this is the pinnacle of that circumstance. (i.e. bloodbending can only be performed under a full moon)
- Water from the Spirit Oasis has unique properties that make it a powerful waterbending tool.
The Avatar Wiki says:
Furthermore, a Waterbender's power is strongest when he or she is situated in colder climates, during the winter, or near their native polar homelands.
I do not recall anything that explicitly demonstrates this in-show.