Ammunition | List of HL2 Animals and Creatures | Mapping with Antlions | Beams and Lasers | Cables and Ropes | Moving Clouds | Color Theory in Level Design | Combat | Combine | Compression (Source 1) | Doors | Dust, Fog, & Smoke | Elevators | Level Transitions | Environmental Lighting, Sun, Weather, & Outdoors | Explosions | Fire | Half-Life 2 Foliage | Glass & Windows | Headcrab | Health | Ladders | Lighting | Optimization (level design) | Physics | Retinal scanners | Sound and Music | Special effects | Terrain | Trains | Turrets | Water | Weapons | Zombie