Use the cursor keys to move Merlin
Hold left mouse button to charge a spell
Point to where you want it to land
Release left button to fire
Please note that you can't fire until you collect the orange scroll at the beginning.
Ctrl - changes the spell Merlin is using
Left shift - toggles Golden Machine Gun on/off (once collected)
NumPad 0 - calls Berlin for assistance
Additionally, you can choose an alternative keyboard layout by clicking on "keys" on the title screen. (I recommend using "qwerty")
"s" - Toggles in-game sound effects
" h" or ESC - Brings up in game menu for saving, loading and help.
To change the difficulty level quit to the title screen and click on "[easy]" at the left of the screen, it will change to "[norm]" and then "[hard]". Then start a new game.