The cloth in the desert is an Easter Egg referring to the protagonist, the wanderer, from the game Way of the Passive Fist. Although getting to the screen with the cloth should also be a screen that kills you, sop we'll look into that for sure
What Halberd are you referring too exactly?
After defeating the fire spirit there's a hidden room just past him.
Yes, some spells are immediate area spells and some require a specific target.
The SUN COIN is used after a series of puzzles in the calming monastery (the palace on the river)