Dota 2 Dark Carnival: Why the Name Doesn't Match

Dota 2 Dark Carnival does not correspond to any confirmed event, cosmetic treasure or game mode. Checking Dota 2's own event history and cosmetic archives turns up nothing by that name.

Where the confusion likely comes from

Dark Carnival is a campaign in Left 4 Dead 2 — a fairground and carnival setting, also made by Valve. Two Valve games, both with community-made cosmetic and event content, is exactly the kind of overlap that produces a search like this one. If that is what you were actually thinking of, it belongs to Left 4 Dead 2, not Dota 2.

What Dota 2 does have instead

Dota 2's own seasonal events have their own names entirely — Diretide and Frostivus among them — none of which are called Dark Carnival. If you're after a specific Halloween-style or festival-themed set, checking the event's actual name is the faster route than searching for this one.

The honest answer

Rather than force a guess to match the search, the plain fact is worth stating: as far as any current source shows, Dark Carnival is not a Dota 2 term.