The Harp is a very rare item that turns all on-screen enemies into slow-falling Mallets, even affecting those who enter the screen during the short-lived effect. Pit will only find this outside of Fortresses. The effects of the harp only last for a few seconds, but transmuted foes will remain as mallets even after the harp stops playing. Transmuted mallets can still be destroyed for Hearts as though they were enemies, but this only applies to mallets created through the harp. Harps will disable a Shemum's Jar from spawning more Shemums until the effect is over.
Any uncollected Mallets will disappear when the Harp's effect ends.
Harps return in this game and perform the same function as in the original Kid Icarus with one major exception. Instead of running on a timer the harps effect now lasts until Pit collects every hammer created by the harp.