Use the following trick to save arrows/bullets and health when facing archers. To kill archers on roofs without being in their line of fire and using up your arrows or bullets, run directly under them where they cannot shoot you and use a Wind spell. It will reach high enough to destroy them in one blow. If another enemy is directly under the archer, you can use a Lightning spell on that target and it will kill the archer directly above him as well. You can now save all but two of your arrows and all of your bullets for the last three Bosses, where they are very useful.