Location : Level pack 2, level X5

If you pan the camera to the lower left edge of the level, you will notice some dancing characters there. Simply rotate the mirror in front of the cannon so that it'll hit them then fire the cannon.

Location : Level pack 1, level 15

You'll need to beat the level in two move.
1. Fire cannon.
2. Move the mirror to its final position once the bullet reach the tile right next to its initial tile, so that the travalling mirror will reflect the charge on its way.

Location : Level pack 2, level X3

So this is about timing. I'll call the moveable vertical mirror, on the left side initially, VM and horrizontal mirror , on the right side initially,HM.

1. Move VM to right above the magnet so charges will be reflect towards HM.
   
2. Fire two charges as rapidly as you can.
   
3. Once both charges hits VM, immediatly move it to the left of robot (right most corner of the loop).
   
4. Once the first charge hits HM, move it above the red charge converter. This should result in the first charge flying towards VM and the second charge got redirect towards red converter while HM moves.
   
5. Once the first(blue) charge hits VM, quickly move it so that it catches and reflect the second(red) charge towards HM as well.
   
6. Let everything settle and you should have six moves left, do the rest the normal way. Three moves to get mirrors in place + one move to fire cannon, resulting in ten moves in total.

Location : Level pack 2, level 20

You'll need to have a lot of charges travelling at the same time. The level is the one I found with a path long enough, there might be other options.
In that level, arrange the five mirrors into a single path and keep firing the cannon.