User:Dinoguy1000/.ydc and .iid files

.ydc and .iid files are used by Yu-Gi-Oh! Online: Duel Evolution, and possibly the other Yu-Gi-Oh! Online titles, to store Decklists.

Each .ydc file is exactly 250 bytes long, and is split into two sections. The first section consists of 80 or 82 bytes of data, corresponding to 40 or 41 internal card IDs stored in hexadecimal, followed by null padding to offset 0xDD (108 or 110 bytes of null padding). The second section, starting at offset 0xDE, consists of additional card IDs storing the Fusion Deck, followed by null padding to the end of the file. The second section may be entirely null.

Built-in Decklists appear to have only 80 bytes of data in the first section; user-specified Decklists appear to have 82 bytes of data (the extra two bytes appear to be an additional card ID but serve an unknown purpose since Decks in the Online series can only be 40 cards in size).

.iid files store only Main Deck data with no padding and are thus always exactly 80 bytes long; other than that, their format is identical to .ydc files.

Both file formats appear to use numerical names, e.g. 7003.ydc or 12001.iid.

Yu-Gi-Oh! Nightmare Troubadour and the Yu-Gi-Oh! Power of Chaos video game series also use files with the .ydc extension, but it is not known if their format is the same or even similar.