Using Notes as attack spells
Note spells are exceptional damage dealers as they have the fastest tick-rate in the game (this characteristic being shared with only a handful of other spells: Giga Death Cross, Summon Deercoy, Spiral Shot, Omega Disk Projectile) while notes are by far the lowest cost.
Tick-rate is amount of damage hits per frame, like piercing.
Notes do not deal damage to the player by default.
Notes are in the "Other" class of spells which means they cannot be used as a trigger, and they do not scale with boomerang spells or concentrated spells perks, however they do gain the damage benefit if paired with normal projectiles.
Notes are very shortlived so the best way to deal damage with them is to increase their lifetime using Orbiting Arc/Spiral Arc/Phasing Arc as they are all no or low cost, which can allow you to make some monstrous machine-gun wands. You will need to grant them damage so keep an eye out for any modifiers. Note that their cast delay can be solved by firing them as a payload from a trigger spell or simply pairing them with a chainsaw (as this drops cast delay of that spell block to 0, make sure chainsaw is last in the cast).