Complex sentence: Boarding their Bison Alien Terrain Vehicle, Scarlet and the others head for Elysium; en route the come across a Bison from Elysium, its three crewmen having died from lack of oxygen while apparently fleeing from their base.
Split into simpler sentences: Boarding their Bison Alien Terrain Vehicle, Scarlet and the others head for Elysium. En route the come across a Bison which came from Elysium, and its three crewmen have died from lack of oxygen while apparently fleeing from their base.