Thank you for playing! Yes, I should've added more things on the map to make it easier to navigate, sorry about that. I originally planed to make some sort of arena for every boss, but was running out of time, and just placed bushes in petal-like formations around bosses. As of secret ending, I can actually give you a spoiler:
You need to kill the skeleton. Since he can't move, I've left only door as an entrance to fireballs, but your lightning strikes at the cursor, and you can use it while circling the shack.