《數碼獸大冒險02：雙人訓練師》（Tag Tamers）於2000年8月在Bandai的WonderSwan掌機推出，是「Tamer 系列」的第二作，同時延續前作《Anode/Cathode Tamer》的設定。補完動畫《數碼寶貝大冒險02》中一乘寺賢與Wormmon的過去與心理變化，也揭開他日後墮落成「數碼獸皇帝（Digimon Kaiser）」的背景，因此在系列粉絲之間擁有特殊地位。

劇情從1999年大晦日事件後展開。主角秋山遼曾在前作中被阿古獸召喚，成功擊敗反派千年獸（Millenniummon）並救回被囚禁的選召孩子們。時間來到2000年夏天，遼造訪好友一乘寺賢的家，卻目擊邪惡數碼獸與太一、阿武兄弟的搭檔激烈交戰。戰鬥暴龍獸與鋼鐵加魯魯在信念的支持下再次站起，合體為奧米加獸，成功擊敗敵人。然而這場危機並未真正結束。幾天後，賢的電腦突然跳出仔獸，告訴兩人邪惡存在尚未消失，於是兩位孩子再度踏上前往數碼世界的冒險。

在本作中，千年獸利用扭曲空間的能力創造出一個個相似卻不同的「鏡面世界（Mirror Site）」，迫使遼與賢分頭行動。要分別操控遼與賢，與仔獸和Wormmon 搭檔，走上各自不同的路線，在各地突破重重難關，最終解救被囚禁的八神太一。遊戲首次描寫賢與Wormmon的相遇，也呈現賢的內心如何逐步被侵蝕，為他轉變成「數碼獸皇帝」埋下關鍵伏筆，為整體劇情增添厚度。

在系統上延續前作的「Tamer 制」，但結構更加複雜。戰鬥採最多三對三的回合制形式，前後衛位置會影響命中率與攻擊力，部分數碼獸甚至有最適合的位置，使隊伍編成更具策略性。裝甲進化與「數碼蛋」也成為系統核心，只要集滿三個碎片即可生成數碼蛋，能提升能力、甚至讓特定數碼獸進行裝甲進化。裝甲形態雖然強大，但僅能攻擊一次，之後便會退回幼年期，考驗玩家使用時機。本作除動畫中的九種數碼蛋外，也追加仁慈、根性、暗黑、欲望等全新類型，使養成方向更加多元。

最具爭議的是「合體進化（ジョグレス）」系統，其複雜程度堪稱系列之最。兩隻成熟期以上的數碼獸可以合體產生更高階的形態，但受限條件極多，尤其究極體所需的合體值高得驚人，往往要反覆合體近三百次才能達成，因此被當時攻略本建議「乾脆放棄究極體」。此外，主角搭檔V仔獸與Wormmon在通關前無法合體進化，導致兩者在中後期火力顯得乏力，也是玩家最常批評的部分。

遊戲地圖分為多個大陸，包括海之大陸、山之大陸、機械大陸與暗黑大陸等，每個大陸需交替操作遼與賢，並對抗不同的頭目，從格雷獸、機械暴龍獸，到黑暗戰鬥暴龍獸與最終的月之千年獸。最終決戰的設計相當特別：後登場的BOSS會「學習」玩家前一場的打法，如果之前使用裝甲進化，下一場BOSS也可能用同樣方式反擊，使難度與策略性大幅提升。

角色刻畫也是本作亮點。秋山遼再次面對宿敵千年獸，一乘寺賢則成為劇情核心，揭露他如何一步步走向黑暗。V仔獸與 Wormmon的個性反差與羈絆也被補充得更完整，尤其Wormmon的溫柔與無法裝甲進化的設定，讓他的處境更令人同情。皮可獸與賢內則在故事中擔任引導者，使世界觀更加完整。

雖然在劇情上補完度極高，但其系統因複雜難解而飽受爭議，尤其合體進化解鎖太晚、究極體取得幾乎不可能、技能平衡混亂等問題，使其成為Tamer系列中難度最高的一作。然而，即便如此，許多老玩家仍視它為系列高峰之一，不只是因為它完整補強賢的故事，也因為它在WonderSwan平台上構築出極具深度的冒險體驗。

對於喜愛《數碼寶貝大冒險02》世界觀的粉絲，《雙人訓練師》依舊是不可錯過的經典作品，在Tamer系列與千年獸主線中都占有無可替代的位置。

“Digimon Adventure 02: Tag Tamers”, released in August 2000 for Bandai’s WonderSwan handheld, is the second entry in the “Tamer Series” and continues the setting established in Anode/Cathode Tamer. This installment not only fills in the missing details of Ken Ichijouji and Wormmon’s past and psychological development from the Digimon Adventure 02 anime, but also reveals the circumstances that eventually lead Ken to fall into darkness and become the “Digimon Kaiser.” Because of this, the game holds a special place among series fans.

The story begins after the events of the New Year's Eve incident in 1999. The protagonist Ryo Akiyama had been summoned by Agumon in the previous game, where he defeated the villain Millenniummon and rescued the kidnapped DigiDestined children. In the summer of 2000, Ryo visits his friend Ken Ichijouji’s home, only to witness an intense battle between evil Digimon and the partners of Taichi and Yamato. WarGreymon and MetalGarurumon, empowered by their unwavering resolve, rise to their feet once more and DNA Digivolve into Omegamon, successfully defeating the enemy. However, the crisis does not truly end there. Days later, Veemon suddenly appears on Ken’s computer, warning the boys that the evil presence still lingers. Thus, the two children embark on a new journey into the Digital World.

In this game, Millenniummon uses his ability to distort space and creates a series of similar yet different “Mirror Sites,” forcing Ryo and Ken to split up. Players must alternate between controlling Ryo and Ken, partnering with Veemon and Wormmon on separate paths, overcoming challenges across different regions, and ultimately rescuing Taichi Yagami. The game depicts Ken and Wormmon’s first encounter and shows how Ken’s mind is gradually eroded, planting the seeds for his transformation into the “Digimon Kaiser,” giving the overall narrative far more depth.

The system follows the “Tamer” mechanics from the previous game but adds greater complexity. Battles take place in a turn-based format with up to three-on-three combat. Front and back row positions affect hit rate and attack power, and some Digimon perform best in specific positions, making team composition more strategic. Armor Digivolution and “Digi-Eggs” form the core of the gameplay; collecting three fragments creates a Digi-Egg, which boosts stats and allows certain Digimon to Armor Digivolve. Armor forms are powerful but can attack only once before reverting to their Baby stage, making timing critical. Besides the nine Digi-Eggs from the anime, new types such as Mercy, Tenacity, Darkness, and Desire are introduced, greatly expanding training possibilities.

The most controversial system is Jogress (DNA Digivolution), widely considered the most complex in the series. Two Champion-level or higher Digimon can fuse into a stronger form, but the requirements are extremely strict. Ultimate-level Jogress, in particular, requires an absurdly high fusion value—often demanding nearly 300 repeated fusions—leading strategy guides at the time to simply advise players to “give up on getting Ultimates.” Additionally, Veemon and Wormmon cannot Jogress before finishing the main story, causing their combat power to fall off significantly in the mid-to-late game, one of the most common player complaints.

The game world is divided into several continents, such as the Sea Continent, Mountain Continent, Machinery Continent, and Dark Continent. Players must alternate between Ryo and Ken on each continent and defeat different bosses, ranging from Greymon and MetalGreymon to BlackWarGreymon and the final boss, Moon=Millenniummon. The final battle is particularly unique: later bosses will “learn” from the player's previous strategy. If the player relied heavily on Armor Digivolution in the earlier fight, the next boss may counter with the same tactic, greatly increasing difficulty and strategic challenge.

Character portrayal is also a highlight. Ryo faces his old nemesis once again, while Ken becomes the emotional core of the narrative, showing how he gradually descends into darkness. Veemon and Wormmon’s contrasting personalities and growing bond are depicted more thoroughly, with Wormmon’s gentle nature and inability to Armor Digivolve making him an especially sympathetic figure. PicoDevimon and Ken’s inner self act as guides within the story, giving the world greater depth.

Although Tag Tamers is highly praised for its narrative expansion, its systems are frequently criticized for their overwhelming complexity. Late-unlock Jogress, nearly impossible-to-obtain Ultimate forms, and unbalanced skill sets make it the most difficult entry in the Tamer Series. Yet despite its flaws, many longtime fans still consider it one of the series’ high points—not only because it fleshes out Ken’s story, but also because it provides a deeply engaging adventure on the WonderSwan platform.

For fans of the Digimon Adventure 02 universe, Tag Tamers remains an essential classic, holding an irreplaceable role in both the Tamer Series and the overarching Millenniummon storyline.