Sciencewater

 a limited-time currency released on June 14, 2016 as part of the Superheroes 2016 Event. It used to heal up to two hearts worth of life to the player's fighters, but only during a battle, be it in the player's town or in the neighbours' town.

It can be obtained,
 * As a drop from Criminals, with a 3% chance of happening.
 * Purchased for 2 Donuts each, but only if the player to heal their fighters without any  remaining.

Packages
Packs containing different amounts could be obtained as prizes:

US$