NeruoToxin + Nurotoxin tubes + Timed dispensors?
Again, the title says it all, what all do I need to do to make this magic happen :3 I'd much rather have it like the boss battle of portal rather than the tubes sliding down to a particular spot.
This is sort of the thing that you just have to think about how to do it. For instance, you can use vactube props for the neurotoxin tubes, and I believe that there is a particle animation for neurotoxin coming out of the tube. For this you need an info_particle_system. There's probably a page of animations on the VDC. For a timer...I don't really know, I'm trying to make a boss battle as well but I don't know how to do this.
Hmm is there any way I can open up the portal 1 and portal 2 maps in Hammer so I can see how they all work? Particularly the boss battles? I would very much like to have a "Finale" like in the main game, to make my side story (well fanfiction lol) have that much more depth.
Actually that's not a bad idea for learning now that I think about it. I should look around at the bsp files and check some stuff out :3
http://ata4.info/bspsrc/downloads.html
decompiles bps' into vmfs to be read by hammer
NOOOOO (heheh, jk. Someone had to say it. 
)
Yes, if you want to look at the official maps, use this program. It's EXTREMELY useful. The SDK even comes with a few pre-decompiled vmfs too, but others can be found in Portal 2portal2maps. You will have decompile these ones though.
Neurotoxic Tubes: there already are vactubes models specifically for neurotoxin gas IIRC. They are similar to the normal ones but the glass reflections are greenish...
Neurotoxin gas: As Toaster Waffles said, you'll need info_particle_systems. These can be activated and deactivated easily firing "Start" and "Stop" outputs to them.
Timed dispensors: here you'll need several entities. As Yishbarr said, the vgui_neurotoxin_countdown is the visual timer seen in Portal2. But this is only the visual part, and can be customized at your wish, check out the example I posted some time ago if you want; it's explained how the timed system works and how to fire whatever outputs on your desired time :p In order to kill the player, I'd go for a disabled trigger_hurt parented to the player onMapSpawn so you can enable it later.
useful tools and stuff here on TWP 
[spoiler]
[/spoiler]
The particle system is called "human_cleanser_cheap"
A map pack coming soon. - click for more information
Okay, can anyone tell me how to make turrets? Like the singing ones in the hidden room?
Put a prop_dynamic turret down, give it one of the "penny_" animations. Put an ambient_generic with the right music down and start playing the sound with a trigger or logic_auto or something.
[spoiler]- BEE2 Addons | (BEE2)
- Hammer Addons
Maps:
- Crushed Gel
- Gel is Not Always Helpful[/spoiler]