How does your submission match the theme?
Lot's of aspects in our game is dual purpose.
There is shoot button, if we tap it for short period of time we fire projectile, but this projectile can't kill one of the enemy (the green one). We can only kill green enemy by charging this button, when player release this button special projectile is fired, only this projectile can kill this enemy. In exchange for that green enemy shoot bullets which are exploding in poisonous cloud, this cloud can kill not only player, but also other types of enemies.
What's else we used curious type of combo system. The more combo value you get (combo resets when you receive damage), the more hp you regenerate killing the enemy. Certain value of combo can turn on triple shoot, this value depends on your hp, the more hp you have - the less combo value you need.
Some of our effects are used not only to looks nice, but also to give feedback to the player. For example due to small screen sizes in mobile there is a great chance that you kill enemy which is off the screen, you will know about this cause of camera shake. If you receive damage screen is becomes red for a while.

Third-party resources
Game engine - Unity 5.6.2
Sounds - sfxr
Photoshop
ScreenToGif
Song - Rhinoceros Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 3.0 License, http://creativecommons.org/licenses/by/3.0/

Contributors
Adrian Sondej (Ardoos), Mirosław Sondej (msondej), Christian Nordgren (Christian Nordgren)