The update to the following article hints that we should be careful about the Ep3 info for a moment, but the Dota 2 part of the leak is certainly real!

http://lambdageneration.com/posts/dota-2-client-leaked-including-actual-hl2-episode-three-code/

Spell icons:

http://www.dota2.cyborgmatt.com/spellicons/

Speech files:

http://www.youtube.com/dota2sounds

Character backstories:

http://www.playdota.com/forums/540621/dota-2-hero-stories-pudge-hooking-tutorial/

Caption... strings...?

http://pastebin.com/ULQDhz3D

Game models:

http://www.dota2.cyborgmatt.com/DotA2_Models.jpg

OMFG HATS?! IN DOTA??

http://i.imgur.com/uNqOC.png

Lastly, here is the supposed HL2E3 leak:

"/src/game/server/ep3/weapon_icegun.cpp /src/game/server/ep3/weaponizer_concrete.cpp /src/game/server/ep3/weaponizer_liquid.cpp /src/game/server/ep3/weaponizer_metal.cpp /src/game/server/ep3/weapon_flamethrower.cpp" If it is real we could see an ice gun, flame thrower, and a... weaponizer in Episode 3. The big news here seems to be evidence of Dota 2's hats and Ep3 info. Shitty wizards...

Shitty Wizards...leaking everything.

Ohhh man, that sucks. Well, sort of. Nowhere near as sucky as the HL2 leak.
 
Weaponizing liquid/concrete/metal sounds pretty cool though.

In before the ARG is discovered.

Shitty wizards

Oh leaks... Valve loves their cataclysmic leaks.

At this point any scrap of episode 3 information is a godsend.

Guys, guys. Come on now, we all know Episode 3 is vaporware.

honestly the most surprising thing THE VALVE HEAD MOVED.

I hate hats FUCK

As much as I would like to believe Episode 3 exists, I would not be surprised if this was Valve's way of trolling everyone because they knew someone would find it.

@Laketown said:

honestly the most surprising thing THE VALVE HEAD MOVED.

When I saw that it pretty much guaranteed me getting no sleep tonight.

@k4el said:

In before the ARG is discovered.

I could go for another Valve ARG.

Valve is laughing. This is exactly what they want.

Goddamn them I can't resist.

Episode 3 is actually just a collection of TF2 hats.

Oh wow some of those placeholder icons are hilarious :3

@isnipeyoudie said:

@k4el said:

In before the ARG is discovered.

I could go for another Valve ARG.

Willing to bet you just got one.

Those are just leftover parts form the canceled Episode 3, they just didn't know where to put it to they swept them under DOTA 2.

I bet Gaben hand picked what to put in that totally innocent folder called ''ep3''

Now, I'm not a DotA player, but... them icons be UGLY.

When will people realize that Half Life 2 Episode 3 is not a real game.

After Portal 2, that absolutely sounds like some HL3 shit right there. Makes me think they looked at Bioshock a little bit as well. Changing the matter state or composition of surfaces? Yes please!
 
"You got your plasmids in my zero point energy manipulator!"