Moth

Barely an enemy. It drifts around the underground jungle slowly, notices you, and floats over to bump into you, and almost anything in your inventory kills it before it arrives. The reason to care is the dust it leaves, which exists for exactly one recipe: Butterfly Wings.

That is the real difficulty. The underground jungle is loud and full of movement, and a slow flier does not stand out in it. A Lifeform Analyzer is the difference between hunting these deliberately and tripping over one every few hours. Without the readout you will fly straight past several.

• The dust does not drop until a mechanical boss is down, so sweeping the jungle right after the Wall of Flesh gets you nothing but banner progress.
• It takes half the usual number of kills to fill in its bestiary entry and unlock the banner, so the grind is shorter than it first looks.