Menderbug

"Member of an elusive guild of bugs fixated on the maintenance of Hallownest's many signs and wayposts. The bugs of Hallownest were obsessed with building things. What strange little minds they had."

Menderbug is an NPC and enemy in Hollow Knight. He can be found repairing the sign at the bottom of the well in the Forgotten Crossroads.

Behaviour and Tactics
Menderbug has a 2% chance to spawn at the entrance of Forgotten Crossroads right below Dirtmouth. To spawn, the following conditions must be met:
 * The sign at the entrance must be destroyed
 * The player must leave and re-enter the room

Upon seeing the Knight, the Menderbug will fly away and quickly leave the room.

To kill Menderbug, enter the Forgotten Crossroads from Dirtmouth using Desolate Dive or Descending Dark. This will destroy the sign upon landing and, if he has spawned, will also kill the Menderbug. He can also be spawned by leaving the room to the west or east within Forgotten Crossroads, however, this method takes significantly more time and makes it easier to miss the kill. One of the easiest ways to catch him is in the late game after acquiring Kingsoul and/or Salubra's Blessing to refill SOUL easily.

Menderbug's Diary
After killing Menderbug, his house will be unlocked. The house can be found in the same village where Sly is first found infected.

Location
Menderbug is located beneath the well in the Forgotten Crossroads.

Trivia

 * There is an unused key found in the game files named Mender_Key and in early dev notes, it is implied that Menderbug would drop this key called an "Odd Key" that would probably then allow access into his house.
 * Killing Menderbug is not needed in order to acquire the Hunter's Mark.
 * Menderbug cannot be read by the Dream Nail.
 * Upon death, Menderbug emits an Infection cloud, despite not showing any hostility like infected creatures do.

References

Починжук Insecto_reparador Majsterobak