Grubberfly's Elegy

Grubberfly's Elegy is a Charm in Hollow Knight. When at full Masks, it causes Nail strikes to fire a projectile which deals 50% Nail damage per hit. Projectiles can pierce enemies infinitely, although they can't do multiple ticks of damage to one enemy.

Usefulness
Grubberfly's Elegy is an effective Nail range upgrade, this Charm is very powerful as a crowd-control tool and when fighting certain bosses such as the Watcher Knights, or Oro and Mato.

This Charm is useful for completing the Delicate Flower quest as it allows for fighting from a distance.

It can be used for exploring areas and switched out for another Charm when fighting bosses. However, during the fight with the Radiance, the projectiles of Grubberfly's Elegy can deal damage to the boss without the need to jump, which can be a viable source of damage when combined with the Quick Slash Charm. This also applies to the Flukemarm fight as the combo makes quick work of her without needing to jump to reach her.

The range of the projectiles is not affected by Longnail nor Mark of Pride, though their height is increased 35% with the latter.

Grubberfly's Elegy can be useful for defeating Radiant difficulty bosses since the Charm's effect is never lost, as being hit results in instant death anyway.

When used with Joni's Blessing, taking damage of any kind halts the effects of Grubberfly's Elegy until resting on a Bench, even if the health is restored by Hiveblood.

How to Acquire
Gifted by Grubfather after freeing all 46 Grubs.

Trivia

 * Grubberfly's Elegy may be based upon the Sword Beam ability from various games in The Legend of Zelda series where being at full health while using your weapon fires out a similar projectile.