WARRIORS OROCHI 3 Ultimate

To get this achievement you need to unlock all the Strategy Cards for use in Duel Mode. There is a total of 294 Strategy Cards. Every character has two cards (a normal card and a gold card) associated with them. Their normal cards are acquired by simply unlocking the character, while the gold cards are awarded for accomplishing specific tasks.

Most characters are unlocked by beating a certain main or side stage in the story, so just keep going through it and make sure to talk to the characters in the camp after every stage you complete, as some of those conversations unlock side stages that may unlock a new character. There are also special "Bond" stages that require you to raise bonds between certain characters and may often unlock a new character as well. When one of those becomes available, you can check it out in the stage select to see the requirements to unlock it if you haven't fulfilled them already. Also worth of note is that the bonds only need to be raised to the second level for those missions to unlock; there is no need to raise them any higher.
While completing all those stages will unlock most characters, there are a few that have special unlock conditions, these are:

Lu Bu - To unlock him you need to play the Battle of Osaka Castle in chapter 3 with Diaochan in your party and when he appears, you must meet up with him before he is defeated.

Gyuki and Dodomeki - To unlock them you need to complete chapter 4 with any ending.

Orochi, Orochi X, Kiyomori Taira, Sun Wukong, Susanoo, Nezha - All of them are unlocked by competing all three endings in chapter 4. The "Good" and "Normal" endings are achieved by clearing "The Demise of orochi X" and "Into the Fire" stages which become unlocked once you are far enough in the story. The "True" ending however is achieved by clearing the "World's End" stage, which is unlocked only once you unlock every other character in the story mode (excluding Hundun and the ones unlocked from chapter five and beyond).

Young Nezha - The alternate version of him is unlocked by clearing "War in the mystic realm" stage in chapter 7 with a recommended team.

Yinglong - he can be unlocked by speaking to him in the camp in chapter 7

Kyubi - To unlock her you need to talk to the guard in the camp after beating chapter 8, which will unlock a new stage in chapter 7. After beating it, talk to the guard again, this will unlock another new stage. Beat it, and Kyubi should be unlocked.

Hundun - To unlock him you need to defeat him in the level 4 of the Gauntlet dungeon, thus clearing the Gauntlet mode for the first time.

Now, after unlocking all the characters you should have all the normal cards. Gold cards however, as I mentioned before have certain requirements that need to be fulfilled before they become available. I will give the breakdown of these bellow.

Unlock Method 1: Set a certain win record in the survival mode.
I do not have the exact table of what card becomes unlocked after what amount of wins; however what I can tell you is that the last card you get is Hundun’s card called “The Origin of Chaos” and it is unlocked after about 90 consecutive wins in survival. If you need help hitting the necessary win streak, check out my guide for the “Survivalist” achievement. The setup I recommend there can easily carry you way past 90 wins. The full list of characters whose cards are unlocked in this manner can be found bellow.
Cao Cao, Taishi Ci, Huang Gai, Zhao Yun, Zhang Fei,
Liu Bei, Sima Sh,i Deng Ai, Wang Yuanji, Xiahou Ba,
Lu Bu, Orochi, Da Ji, Sun Wukong, Kiyomori Taira,
Orochi X, Dodomeki, Gyuki, Kaguya, Shuten Doji,
Susano'o, Ryu Hayabusa, Ayane, Achilles, Momiji,
Tamamo , Kyubi , Hundun , Nobunaga Oda, Shingen Takeda,
Hanzo Hattori, Tadakatsu Honda, Nagamasa Azai, Kanetsugu Naoe,
Kiyomasa Kato, Motonari Mori, Aya, Masanori Fukushima.

Unlock Method 2: Defeat certain characters in duel mode (offline or online). If you play against the AI the difficulty does not matter.
Xu Zhu, Zhang He, Cao Ren, Cao Pi, Cai Wenji,
Pang De, Zhou Yu, Sun Shangxiang, Sun Jian, Ling Tong,
Xiaoqiao, Zhuge Liang, Wei Yan, Liu Shan, Sima Yi,
Dong Zhuo, Zhurong, Zuo Ci, Fu Xi, Nuwa, Yoshitsune Minamoto,
Benkei, Nezha (Cyborg), Joan of Arc, Nemea, Yinglong,
Keiji Maeda, Kenshin Uesugi, No, Ranmaru Mori, Sakon Shima,
Toshiie Maeda, Katsuie Shibata, Kai, Goemon Ishikawa, Kojiro Sasaki.

Unlock Method 3: Maximize the proficiency level of certain characters in Story Mode.
Xiahou Dun, Zhang Liao, Xu Huang, Zhenji, Jia Xu,
Zhou Tai, Sun Ce, Sun Quan, Daqiao, Ding Feng,
Guan Yu, Ma Chao, Xingcai, Ma Dai, Bao Sanniang,
Xu Shu, Sima Zhao, Zhuge Dan, Guo Huai, Zhang Jiao,
Taigong Wang, Himiko, Nezha (Human), Yukimura Sanada, Oichi,
Kunoichi, Masamune Date, Hideyoshi Toyotomi, Ieyasu Tokugawa, Mitsunari Ishida,
Yoshihiro Shimazu, Ginchiyo Tachibana, Nene, Motochika Chosokabe, Kanbei Kuroda, Ujiyasu Hojo, Hanbei Takenaka.

Unlock Method 4: Clear character-specific side stages on Hard or Chaos.
Namely, these stages are:
• Breakthrough at Guangzong
• Battle of Nanjun
• Salvation at Nagashino
• Liberation of Luo Castle
• Battle of Hefei
• Battle of Mikatagahara
• Retreat from Mt. Niutou
• Rescue at Taoshui
• Battle of Tetorigawa
• Battle of Jieting
• Battle of Komaki-Nagakute
• Chaos at Tetorigawa
• Diversion at Mt. Xingshi
• Battle of Mt. Niutou
• Siege of Luoyang
• Siege of Tong Gate
• Battle of Jiange
• Purge of Nanzhong
• Battle of Taoshui
• Ambush at Kyushu
• Struggle for Ueda Castle
• Battle of Jiangdong
• Defense of Yangping Gate
• Battle of Yan Province
• Battle of Xu Province
• Battle of Liaodong
• Defense of Jieting
• Battle of Luo Castle
• Heroes of Komaki-Nagakute
• Battle of Liang Province
• Rescue at Yiling
• Siege of Shouchun
• Battle of Guangzong
• Rescue at Dongkou
• Battle of Mt. Xingshi
And here is the list of characters whose cards you unlock.
Dian Wei, Xiahou Yuan, Wang Yi, Guo Jia, Lu Xun,
Gan Ning, Lu Meng, Lianshi, Huang Zhong, Guan Ping,
Pang Tong, Yueying, Jiang Wei, Guan Suo, Zhong Hui,
Diaochan, Yuan Shao, Meng Huo, Sanzang, Seimei Abe,
Rachel, Shennong, Kasumi, Sterkenburg, Sophitia,
Mitsuhide Akechi, Okuni, Magoichi Saika, Yoshimoto Imagawa, Ina,
Kotaro Fuma, Gracia, Musashi Miyamoto, Muneshige Tachibana.

So this should be everything you need to unlock the achievement. This was a bit of a rough one to put together so hopefully I didn’t get anything mixed up or leave anything out. This is one of the more difficult achievements and will take a while to get, so good luck and try to have fun.