[Spoilers]
I finished the game today. I was stucked on level 5 for pretty long. The reason why I think i did is that you introduced two new things at once: new type of enemy and position swap cards. It was clear that you needed to use new card on the new type of enemy. But the execution was not clear. You needed to time the swap perfectly so the enemy killed itself. You should introduce the new mechanics in preceding level where is absolutely clear what the new card do.