i was in infected crossroads ...

[Steve Magal]

i was in infected crossroads when i found a ¿mailman? that was weird , i never see it again , what is?

[Ellixer]

I believe that's the Menderbug. I never ran into him so I can't tell you much, but you can check the wiki if you're curious.

[SelectBard133]

Menderbug is a rare bug that will occasionally appear after you have broken the sign beneath Dirtmouth, left the area, and returned. In order to complete the Hunter's Journal you need to kill him

[Ellixer]

He has a journal entry, but you don't need to kill him if you want the achievement. Which is good, cause I felt bad enough having to (accidentally) kill the maggots to complete it.

[Darc Vader]

Originally posted by Ellixer:

He has a journal entry, but you don't need to kill him if you want the achievement. Which is good, cause I felt bad enough having to (accidentally) kill the maggots to complete it.

Same with the final boss and everything added with the content packs

[klimat13]

Basically Menderbug is a part of a secretive guild of repair bugs who would repair all the background stuff you can destroy on levels. You can bait him to show up by destroying a sign in Forgotten Crossroads that is right below the exit to Dirtmouth, also he will run away fast as soon as he sees you. You can kill him by destroying said sign and re-entering Forgotten Crossroads from Dirtmouth by doing Desolate Dives multiple times, killing Menderbug will open his house at the bottom of Forgotten Crossroads near Sly's old home, there you can read Menderbug's journal, which will make you feel like a a complete monster for killing the poor guy, so please don't do it.

[Hedgelord, Lord of Hedges]

Originally posted by SelectBard133:

Menderbug is a rare bug that will occasionally appear after you have broken the sign beneath Dirtmouth, left the area, and returned. In order to complete the Hunter's Journal you need to kill him

Menderbug is not needed to recieve the Hunter's Mark.