《伊蘇IX -怪人之夜-》(Ys IX: Monstrum Nox)是由日本Falcom開發並於2019年率先在PlayStation 4推出，之後陸續移植到PC、Nintendo Switch、PS5等平台的動作角色扮演遊戲，是《伊蘇》系列的正統續作。故事延續系列主角亞特魯·克里斯汀（Adol Christin）的冒險傳奇，但場景從廣闊的荒野與古代遺跡，轉移到一座充滿陰謀與神秘氣息的監獄都市「巴爾鐸克（Balduq）」。在劇情與玩法上都帶來顯著變化，更強調都市探索與特殊能力運用，並融入半開放世界設計與多角色戰鬥系統。

劇情方面，亞特魯與多奇(Dogi)在前往巴爾德克的途中因過去事蹟而被捕入獄，在牢中遇見一名神秘的紅髮女子「亞普莉莉絲（Aprilis）」，並被她施加詛咒，成為擁有特殊力量的「怪人（Monstrum）」。這股力量賦予亞特魯與其他幾位怪人超自然能力，但也迫使他們無法離開都市邊界，並必須對抗來自異界「格林姆華爾（Grimwald Nox）」的魔物入侵。隨著劇情推進，將逐步揭開巴爾德克的歷史黑幕、異界與現實的連結，以及怪人力量背後的真相。每位怪人都有自己的背景故事與內心掙扎，主線與支線交織，呈現充滿懸疑與情感衝擊的劇情體驗。

在操作與戰鬥系統上，延續《伊蘇VIII》的高速動作戰鬥風格，但引入「怪人能力（Monstrum Gifts）」的新要素。在探索都市與迷宮時，可自由切換控制不同的怪人角色，每位角色擁有獨特的移動與探索技能，例如「滑翔」、「攀牆」、「瞬間移動」等，讓關卡設計更加立體化。戰鬥採用即時制的高速連擊系統，並保留系列招牌的「屬性相剋」、「閃避反擊（Flash Move）」與「格擋反擊（Flash Guard）」機制。透過角色切換，能靈活應對敵人的弱點，並累積必殺技槽施放強力的「EX技能」。此外，還引入「格林姆華爾之夜」防衛戰模式，必須保護據點免受成群魔物攻擊，這類戰鬥節奏緊湊且考驗隊伍協作。

市場評價方面，在日本與海外皆獲得普遍正面評價。日本媒體《Famitsu》給予 35/40，稱讚遊戲在都市探索上的創新、角色塑造的深度，以及戰鬥系統的爽快感。歐美媒體如IGN與RPG Site也給出8分左右的評價，認為本作在動作性與劇情氛圍上表現出色，尤其是「怪人能力」讓探索過程更具樂趣。然而，也有部分評論指出，由於場景集中在都市內，與《伊蘇VIII》相比少壯闊自然景觀的開放感，且初期劇情節奏稍顯緩慢，需要耐心投入。

整體而言，《伊蘇IX -怪人之夜-》是將系列傳統的高速戰鬥與全新都市探索結合的作品，故事氛圍更偏向黑暗與懸疑，角色互動與支線劇情塑造濃厚的人情味。對於喜愛動作RPG的玩家來說，不僅延續《伊蘇》系列的流暢打擊感，也嘗試拓展玩法邊界，是值得一試的高品質日式動作角色扮演遊戲。

Ys IX: Monstrum Nox is an action role-playing game developed by Nihon Falcom, first released for PlayStation 4 in 2019, and later ported to PC, Nintendo Switch, and PS5. It is a direct sequel in the Ys series, continuing the legendary adventures of series protagonist Adol Christin. Unlike previous entries that focused on vast wildernesses and ancient ruins, the setting shifts to the prison city of Balduq, a place steeped in intrigue and mystery. The game brings notable changes to both story and gameplay, placing greater emphasis on urban exploration, special abilities, and a semi-open world structure combined with a multi-character combat system.

The story follows Adol and his companion Dogi as they travel toward Balduq, only for Adol to be arrested due to his past exploits. While imprisoned, he encounters a mysterious red-haired woman named Aprilis, who curses him and transforms him into a Monstrum, granting him supernatural powers. These powers bind him within the city limits and force him to battle creatures from an alternate dimension known as the Grimwald Nox. Alongside other Monstrums, each with unique abilities and personal struggles, Adol is drawn into a web of events that gradually reveal the dark history of Balduq, the link between the otherworld and reality, and the truth behind the Monstrum powers. The narrative intertwines main and side quests, delivering a suspenseful and emotionally engaging experience.

In terms of gameplay and combat, Ys IX retains the fast-paced action style of Ys VIII while introducing the new “Monstrum Gifts” mechanic. Players can freely switch between different Monstrum characters, each possessing unique movement and exploration abilities—such as gliding, wall-running, and teleportation—that make the level design more vertical and dynamic. Combat remains real-time and combo-driven, with the signature Ys mechanics of elemental weaknesses, Flash Move (perfect dodge), and Flash Guard (perfect block) intact. Switching characters in battle allows players to exploit enemy weaknesses efficiently, while building up a special gauge to unleash powerful EX Skills. The game also features the “Grimwald’s Night” defense missions, where players must protect a base from waves of monsters in fast-paced, cooperative-style battles.

Upon release, the game received generally positive reviews both in Japan and overseas. Japanese gaming magazine Famitsu awarded it a 35/40, praising its innovative approach to urban exploration, the depth of its character development, and the satisfying feel of its combat system. Western outlets such as IGN and RPG Site gave it scores around 8/10, highlighting the engaging action and immersive atmosphere, with the Monstrum abilities adding significant enjoyment to exploration. However, some critics noted that the confined urban setting lacked the expansive natural vistas of Ys VIII and that the early pacing was somewhat slow, requiring patience before the story’s full momentum is felt.

Overall, Ys IX: Monstrum Nox blends the high-speed combat the series is known for with a darker, more suspense-driven narrative and fresh urban exploration mechanics. It maintains the fluid, satisfying action fans expect while pushing the series in new directions. For players who enjoy action RPGs, it offers a high-quality, emotionally resonant adventure that expands the boundaries of what a Ys title can be.