Extensions are weapons in My Crypto heroes. One hero can equip up to two Extensions. Then, Hero status is enhanced and special skills can be activated.
Original Extensions are NFT and tradable in the GUM market or Secondary Market, such as OpenSea. Like Heroes, they have "Rarity" and "Lv".
Replica extensions are copies of original items and not NFT. They are much easier to get. However, you can't trade it, level up it. Also, it expires after 7 days.
Original Extensions have the total supply limit.
For more information, please see the help.