It was by design. Lightning did more damage to the bats and frogs, and fire did more damage to the monkeys. For the lizard boss, you do more damage with lighting when it's health was yellow, but more with fire when it was red. The Octopus boss had a mechanic that I didn't have time to show in game, but you have to damage it with a ice to freeze the 'skin', then hit it with the fire and it resets every time it moves. I didn't have time to show that in the sprites, but the mechanic was there. Thanks for the compliment on the art!