This game was one of the first to implement the "branching path" game mechanic. Throughout the course of the game, players are given numerous situations in which their actions will have an effect on the direction of gameplay. For instance, in the beginning of the game, a male civilian is about to be thrown off the bridge to his death. If players shoot the zombie and save the civilian, they will enter the house directly through the front door. However, if the civilian dies, players are redirected to an underground route through the sewers. There are other critical points in which the players' actions decide where they go. This branching path system was also implemented in subsequent installments to the series.
Amidst the chaos wrought by Curien, Rogan and "G" face many formidable foes, including The Chariot (Type 27), a plated undead warrior who mortally wounds Sophie (whether she survives the wound or not depends on player performance upon beating the game), The Hangedman (Type 41), a gargoyle-like creature which sees to it that she cannot escape the mansion grounds, as well as The Hermit (Type 6803), a mutant spider crab guarding the passageway leading to Curien's restricted research area.
Upon confronting Curien, the AMS agents are treated to his greatest masterpiece, The Magician (Type 0), a humanoid creature with mastery over fire. Ironically, after he releases the creature from its incubation chamber, Dr. Curien is killed by his creation; "The Magician" seemed to have reached a state of sentience in which he feels an inferior being such as a human has no place in giving him instructions. To prevent the Magician from escaping the mansion and destroying the world, Rogan and "G" killed it before any harm could be done.