A dupe is a glitch that makes an item appear twice when it is passed to another player. MM2 players say "duped?" about an item the way a coin collector says "replica?". It matters because rarity is what makes most items valuable, and a dupe turns a rare item into a common one overnight.
If you came back after a few years and someone told you your old knife is "duped", this page is the context.
Timeline of the major dupes
2017: the Duping Glitch, aimed at Corrupt
The main target was Corrupt. Before 2017 there were around 63 owners of Corrupt, all from the Data Loss Glitch of 2014. After the dupe there are thousands of copies. Trading and trade servers were closed for a while, and accounts holding 100 or more of an item were banned.
2019: Season 1 Chromas, Chroma Gingerblade and Boneblade
The next wave hit the first Chromas: those from Season 1 and the 2018 box Chromas such as Chroma Gingerblade and Chroma Boneblade. Old Chromas from 2018-2019 lost value after what the wiki calls the Duping Glitch of 2019.
2021: Batwing and the Discord giveaways
Batwing was duplicated and handed out in Discord giveaways. Nikilis, the game's developer, banned players who held 190 or more Batwings.
2021: the Candleflame Glitch
A separate glitch the same year hit Harvester and Candleflame.
2022: Icewing and shop items
Icewing and a set of items sold in the shop were duplicated. This came after trading had already been limited to level 10 and above, which has been the rule since 28 December 2021 as a measure against dupes.
How dupes changed values
Two things happen after a dupe.
The hit item drops. Old Chromas from 2018 and 2019 are the clear example. A comment under a 2025 video makes the point from the other side: new godlies that came out after the dupe era trade for thousands, while small godlies from before it are worth under a hundred. That is one player's observation, not a table, but it matches what you see in the godly values.
The market gets nervous. Players also say the market dipped in 2025 because there were no new weapons, and that dupes and a black market feed it. When people suspect new copies, demand for old rare items drops, even for honest owners.
Bans take copies out too. A banned holder of 190 Batwings is 190 copies gone from the market.
How to tell if an item is duped
I do not know a visible mark in the game that says "this copy is duped". What you can do is work from the item and the history.
- Check the item against the dupe list above. If it is Corrupt, an old Chroma, Batwing, Icewing or Candleflame-era item, assume copies exist.
- Ask where the item came from. An honest owner knows: a box, an event year, a trade with a name.
- Know that the community marks it. Old players say things like "the rest are duped but still have a bit of value". A marked copy sells for less.
- Look at the owner. A single account with dozens of one rare item is a signal, because accounts with too many Corrupt (more than 20) get banned on rejoin.
- Price it lower if unsure. Check the trade calculator and discount.
If you are returning after years, the question "is my inventory worth anything" has the same answer: check each item on the inventory calculator, and treat any item from the dupe list with extra care.
Why this matters now
Dupes are behind two rules you meet today: the level 10 limit for trading and the ban for holding more than 20 Corrupt.
They are also the reason an old item and a new item with the same look can have very different values. The one with a clean history wins.