We've found a bug that can unlock the "All Fairies Gathered" achievement even when not all fairies have actually been collected.
We believe quite a few players may have already unlocked this achievement because of this bug. Unfortunately, once a Steam achievement has been unlocked, it cannot be removed. We apologize for the confusion.
We'd also like to explain the behavior that allows players to pass through walls while invincible.
This is actually intentional. In the Level 17 scrolling stage, it prevents a situation where the player loses their armor from being crushed by a wall and then immediately takes additional damage before having a chance to recover.
However, when this behavior occurs in unintended places, such as the CLIFF stage, it can cause the player to become embedded in terrain and get stuck. To avoid that problem, the game will now immediately deal damage when invincibility wears off while the player is inside a wall.
We apologize for the inconvenience, and thank you for your continued support and understanding.