Nice game! The art is fantastic, and the gameplay is simple and easy to understand!
I think toggling the sprite of the hero's sword would really help make the game more intuitive. That, and maybe changing the sounds of the sword swing depending on what sword is equipped? (a fwoosh for the fire, a rumble for the grass, and like a frozen sound for the ice)
I also think arranging the sword buttons in a triangle might be a clearer way to help players remember the advantage system
Well done!