First of all, thank you so, so much for your thorough feedback. It is extremely appreciated!
I was also thinking about doing some invincibility shenanigans, but was not able to do it in time. But I will probably tackle that in the future. I also really like the idea of recalling the arrow, though this would need some big balancing, like a cooldown or so. But a really cool idea!
Regarding the "other way" of ending the game. It is more like a gimmick than an actual way to play the game. If you win the game once, you will get a hint at what the hidden feature is. Please don't expect too much, though! I will definitely tweak this feature in the future, plus add more variety to it. I won't go into too much detail, not to spill the secret ^^
So yeah, thanks so much for the helpful criticism and the nice feedback. It is highly appreciated ^^