"One Dangerous Zombie" is a feature for the "REmake" in which it is unlocked by completing Jill Valentine and Chris Redfield's scenarios twice (playing "once again" for both characters). In the HD remaster, it is unlocked by completing Chris and Jill's scenarios once on normal or hard difficulty.
Forest will be present in various locations throughout the mansion during the first section of the game, replacing a regular zombie in most areas. He should be avoided at all times, and the player may consider taking another route if possible.
Forest cannot be killed without also killing the player and resulting in a game over, as he has grenades strapped to him which will explode if attacked. In addition, defense items such as the dagger, flash grenade, and stun gun are unable to be used on Forest so the player must take damage if grabbed by him.