Trying it out, got a suggestion for you, when you get a powerup you should have some kind of indication on the player that they are under the effects of the powerup, so it isn't such a surprise that 1. that actually did something, and 2. the effect ended. Like maybe make the wand blink or some sparkle effect or something.
It's kind of amusing but it feels like the easiest answer to every puzzle is "block tower".