and energy weapons, to "Beheaded Kamikazes" who charge at the player while screaming loudly until they explode, to more powerful alien foes such as charging bulls, alien robots with rockets and miniguns, and creatures made of lava that can split themselves into smaller enemies upon death. The player can carry a number of weapons such as twin revolvers with unlimited ammo, shotguns, a minigun, a rocket launcher, a quad laser gun, and a cannon that can kill multiple enemies at a time. Ammunition is scattered across levels that the player must pick up to reload, but players can also explore the level's environments to find secret items including more health, ammo, and weapons that they might otherwise only find later in the game. Unfortunately, some items are planted as bait for traps and may trigger a spawn of more enemies when the player collects them. The game features cooperative gameplay through a split-screen mode and via the internet. Plot In ancient times, Earth was involved in a massive conflict between Mental, an evil extraterrestrial being who seeks to conquer all life in the universe, and the Sirians, a technologically advanced race of humanoid aliens. Although the Sirians were ultimately defeated, they left behind remnants of their advanced technology, which were later discovered by modern humans at the dawn of the 21st century and used to develop the means for human civilization to explore other galaxies and establish many interstellar colonies. In the 22nd century, Mental suddenly reappears and leads his vast army of aliens from planet to planet, destroying every colony until he finally reaches Earth. As a last resort, humanity's leaders decide to use the "Time-Lock", an ancient Sirian artifact that contains the power to send a single person back to a chosen point in time. Sam "Serious" Stone, a soldier whose bravery in fighting the aliens has made him a living symbol of human resistance, is recruited to go back in time to when Mental was fighting the Sirians in the hope that he might find a way to eliminate Mental and change the course of history. As the game opens, Sam appears in Egypt during the time of the Pharaohs, guided by an AI called NETRISCA. He visits several locations, including the Valley of the Kings, to collect religious icons representing the four elements of Water, Earth, Air, and Fire while battling hordes of aliens sent by