Grubberfly's Elegy is a Charm in Hollow Knight. When at full masks, it causes Nail strikes to shoot a projectile which deals 50% Nail damage per hit.
Usefulness
This charm is useful for completing the Delicate Flower quest as it allows for fighting from a distance and detonating the explosive bubbles found in Fog Canyon.
It can be used for exploring areas and switched out for another charm when fighting bosses. However, during the fight with the Radiance, the beams 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 Quick Slash. This also applies to the Flukemarm fight as the combo will make quick work of her without the need to jump in order to reach her.
The range of the projectiles is not affected by either Longnail nor Mark of Pride.
Grubberfly's Elegy can be useful for defeating 
Radiant difficulty Bosses since there will be no loss of the Charm's effect, as being hit results in instant death.
When used with Joni's Blessing, taking damage of any kind will halt 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.
Charm Interactions
 | Fragile Strength Stacks multiplicatively with Fragile Strength, producing 76% Nail damage (rounded up) per projectile. 4/7/10/13/16 damage per Nail upgrade 0/1/2/3/4. |
 | Fury of the Fallen Fires red projectiles at one health, producing 70% Nail damage (rounded down) per projectile at one health. Note that this works only when the Knight has only 1 mask left (No projectiles will be sent at 1 mask if Fury of the Fallen is not equipped). This effect will not take place if the Knight has any lifeblood. 3/6/9/12/15 damage per Nail upgrade 0/1/2/3/4. |
 | Grubsong When used in combination with Grubsong, the amount of SOUL received from taking damage is increased by 10 (to 25 SOUL). |
 | Mark of Pride Increases the size of the projectiles from Grubberfly's Elegy. |
 | Lifeblood Heart Grubberfly's Elegy only counts mask health as full health, so by using Lifeblood health (except those gained from Joni's Blessing), taking damage will not remove Grubberfly's Elegy's effect. |
 | Lifeblood Core Grubberfly's Elegy only counts mask health as full health, so by using Lifeblood health (except those gained from Joni's Blessing), taking damage will not remove Grubberfly's Elegy's effect. |
 | Hiveblood Taking damage and then regenerating it with Hiveblood will restore Grubberfly's Elegy's effect. However, this will not work in combination with Joni's Blessing. |
 | Note: Using Grubberfly's Elegy in combination with Fragile Strength and Fury of the Fallen results in giving the projectile ~114% Nail damage. 6/10/15/20/24 damage per Nail upgrade 0/1/2/3/4. |
Trivia
- After all of the Grubs are freed and this charm is obtained, resting at a bench and visiting the room again will reveal that the Grubfather has eaten all of his children. The name of the charm, Grubberfly's Elegy, could be foreshadowing this since an "elegy" is typically a poem mourning the dead. However, it is possible that the Grubfather is actually protecting his children by serving as a cocoon for them to metamorphose. This is supported by the description of the charm and the name of the achievement for rescuing the Grubs, "Metamorphosis". In that optic, the "Elegy" could be for the Grubfather, since upon completing their transformation his children will presumably burst out of him, killing him, similar to the Gruz Mother.
- The effect of Grubberfly's Elegy may be inspired in some games of the Legend of Zelda series, where the protagonist, Link, is able to shoot beams out of his sword when he is at full HP.
