Forbidden Siren 2, known in Japan as Siren 2 (サイレン２ Sairen Tsū), builds upon that of its predecessor, Siren, with some significant improvements, namely the ability for characters to crouch-walk, a proximity alert that warns the player of nearby enemies, a hint system that guides the player to the current mission objective, three selectable difficulty levels, and an optional first-person mode. Context-sensitive interactions now require only a single button press when prompted, and bringing up the in-game menu for common interactions no longer pauses the game. Important items remain in the inventory after restarting a scenario.
The "sightjack" system has been improved by allowing the player to automatically sightjack nearby enemies. Character-specific features have also been incorporated, such as Shu Mikami's ability to move while sightjacking due to his near blindness, Ikuko's ability to control sightjacked enemies, and Akiko's ability to reveal psychic impressions when sightjacking in certain areas.
In contrast to the mainly stealth-based tactics of the previous game, players can now freely choose between stealth and action. The new combat system introduces a three-hit combo attack. Characters are also able to attack barehanded (although extremely weak and only effective to repel attackers in order to run away). Characters may also use guns as melee weapons. Many more weapons are available for each character, with many of them being improvised.
The shibito are slightly faster, more aggressive, and more intelligent than they were previously. However, they are still just as easy to distract from their usual habits. Once defeated, they revive only when a shiryo (屍霊 shiryō, lit. "corpse spirit") re-enters the corpse. The player can prevent a shibito from being revived by eliminating the shiryo with a weapon hit or flashlight.
A new type of enemy is introduced, called the yamibito (闇人 yamibito, lit. "darkness people"), which, although much more resilient, aggressive, and intelligent than the shibito, function essentially the same way. They are also repelled by light, meaning that they can be weakened by focusing a flashlight on them or turning on the lights in a room. Like the shibito, a yamibito can be defeated, but is revived when a yamirei (闇霊 yamirei, lit. "darkness spirit") re-enters the corpse. Eliminating the yamirei (which are also intolerant to light) renders the yamibito unconscious indefinitely. However, due to their improved intelligence and strength, yamibito will not fall for distractions that may have worked on shibito, and they are also much harder to defeat in combat.
Source: Wikipedia, "Forbidden Siren 2", available under the CC-BY-SA License.