I only have one, very small, suggestion: The vertical (left-bounding/right-bouncing) mirrors are harder to identify than the horizontal (up-bouncing/down-bouncing) ones. You should probably introduce the player to the latter first.
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Thank you for playing! I have to agree with you very much on that.
The thing is, that the mirror textures got changed in like the very last day of the jam. Before the mirror upgrades (you can see the old design in the menu backgrounds), it was a lot more clear on what mirror does what.
After the mirrors got changed I had no time for playtesters and so I couldn't change the mirrors or change level 4