Ok. These require good hacking (scripting/ console smarts)open the console (~) and type in sv_cheats 1. Once you do that, you can type in some things. Here are a few:
npc_create npc_ (name of npc): allows you to spawn any npc, such as a citizen, combine soldier, alyx, barney, metropolice, zombies, headcrab, ect. LIST OF NPC: combine_s (soldier) citizen, headcrab, zombie, fastzombie, zombine, zombie_torso, metropolice, headcrab_fast, headcrab_black, headcrab_poison, and vortigaunt. These are the most useful things. Now, if you want them to have a weapon, (metropolice, combine_s, and citizen can only have guns. ) before the npc_create npc_, type in npc_create_equipment weapon_ (name of gun, shotgun, pistol, smg1, ar2) and boom! Npc war if you spawn a bunch of things! Only problem, some weapons aren't compatible with the model, so they wont hold it, it will float in front of them, or they wont fire it at an enemy. (example of float: 357 with citizen, example of not shooting at enemy: metropolice with shotgun)and if you want the npc to patrol a area, type in ent_fire npc_ (name of npc) start patrolling. That is all the cheats I can tell. For now keep looking back for more that I post.