[Looking for the name of a mod pack]

Here's a re-creation of what they are using plus some of the mods suggested in the comments:

http://www.technicpack.net/modpack/details/yogcraft-147-yogscast-pack.156638

[Help with pipes]

Don't smelt ore blocks; make an Applied Energistics Grind Stone and Wooden Crank. Just 3 quartz dust, 3 stone/smelted-cobble, 2 cobble, and 4+5 sticks for double ores. Don't abuse the crank with the grind stone empty; I've had it break, losing a few sticks.

[UPSIDE DOWN MADNESS]

F11 just stretches the window to fill the screen. You have to select Full Screen Mode within Hexxit/Minecraft. Options/Video Settings.../Fullscreen: OFF.

[Mysterious tree]

Really? Mine is empty, completely. The strange thing is, it didn't generate at all. I walked over that path several times, and it wasn't there before... I did hear a meteor sound, so I thought this caused it, but that can't be it, right?

Sounds like it could be qCraft.

[Hexxit Startup/Hexxit MineCraft]

Try full screen. I've heard it works.

How to Fix Your Technic Launcher (crash bug + upsidedown screen bug) on Mac OSX

[I can't do anything!]

You set it to Adventure Mode, rather than Survival or Creative?

[Hard Mode?]

Make all mobs infernal and make the tougher versions rarer.

[Dungeon Tower Spawned, Home Destoyed]

From Hexxit wikia:

A Battle tower may spawn at where your house was, deleting all your loot and hard work if you return from a dimension, this is caused by chunks error because of teleporting from one to other dimension.

What causes chunk errors?

Rapid approach to a portal?

[ID mismatches]

<user>/AppData/Roaming/.technic/hexxit/Chocolate

I'd move the Chocolate folder and see if it gets replaced. Or its contents.

[Which mod is doing these things?]

<FTB launcher folder>/<FTB modpack folder>/minecraft/config/TinkersWorkshop.txt

[Lost my dimension, and essence crystals?]

I think there are bushes that grow Essence, similar to the berry bushes or the ore berry bushes.

[Dungeon Tower Spawned, Home Destoyed]

Blocks from Secret Rooms cause this.

This is terrible. You think to build a secret room for your best stuff, and it gets destroyed, because you hid it in a secret room.

[I cant seem to change my mode!]

Image search for Not Enough Items, find the Options screen.

Hide/Show: O

Press the O key.

[Lumber Axe bugged]

Yep, it's bugged. I throw them into cacti to keep them from accidentally being used. It's safer than lava.

[Black haze]

"Yes."

If you want a challenge you can try making Rift Remover(s) and see if you can kill them faster than they spread.

Minor Operator mode:

In config/DimDoors.cfg change B:"Enable Rift Spread"=true to =false, and maybe B:"Enable Endermen Spawning from Rifts"=true to =false, at least during the removal.

Then use the Rift Remover(s).

(I don't know if Rift Removers are reusable or not.)

config/DimDoors.cfg is located in your server folder or in Windows <user>/AppData/Roaming/.technic/hexxit/.

[How do i solve the Internal Server Error]

It crashed during the Scouter update.

http://hexxit.wikia.com/wiki/Scouter says the Scouter causes crashes and an NBT-editor can be used to get rid of the Scouter.

[T-construct secret tools]

Don't you see "<poster>, <time of post> Report" at the bottom of each post?

That's what I was talking about. It's effectively signing the post with the username of the poster.

[T-construct secret tools]

The posts are autosigned.

sig below:

[MASSIVE amounts of entities being spammed?]

There could be a rift storm within the chunks that Minecraft has loaded. (view-distance=10, center chunk plus 10 chunk radius?)

[Black haze]

Probably talking about a rift storm. Only rip one hole in reality at a time, then slap the right kind of door on it.

I'm rethinking making compact portal rooms for a transportation network. One creeper and you could get a rift storm in your base. :(

[HEXXIT KEEPS CRASHING!!!!]

Click Edit, [Edit: It's between the auto-signature and Report]. Then click "More Options..." in the pop up.

Try increasing PermGen/PermSize.

-XX:MaxPermSize=256M or higher, in a server launch command. The top right gear in the launcher, then the increase PermGen checkbox.

[Server Not loading, after a while stuck on Loading NEI]

I've been seeing MCP a lot in these crash reports. Try increasing MaxPermSize.

Add -XX:MaxPermSize=256M or even more to the launch line.

Example: java -Xmx3G -Xms1G -XX:MaxPermSize=256M -Xincgc -jar Hexxit.jar nogui

Classes go in the Perm. Not enough Perm, missing classes?

[hexxit crashes after the mjang label???]

Or try increasing PermGen. The gear in the top right of the launcher shows you a check box for increased PermGen. PermGen is were the classes from each mod go. It's default max is only 32MB client and 64MB server.

[Hexxit Closes Unexpectedly During Play]

You could try updating lwjgl.

It says it crashed in native code. That would be not J or j, but v.

Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)

j org.lwjgl.openal.AL10.alSourcei(III)V+0

j paulscode.sound.libraries.ChannelLWJGLOpenAL.attachBuffer(Ljava/nio/IntBuffer;)Z+39

j paulscode.sound.libraries.SourceLWJGLOpenAL.play(Lpaulscode/sound/Channel;)V+364

j paulscode.sound.Library.play(Lpaulscode/sound/Source;)V+72

j paulscode.sound.Library.play(Ljava/lang/String;)V+93

j paulscode.sound.SoundSystem.CommandPlay(Ljava/lang/String;)V+12

J paulscode.sound.SoundSystem.CommandQueue(Lpaulscode/sound/CommandObject;)Z

J paulscode.sound.CommandThread.run()V

v ~StubRoutines::call_stub

[Crash report]

Add -XX:MaxPermSize=256M to the launch line.

Example: java -Xmx3G -Xms1G -XX:MaxPermSize=256M -Xincgc -jar Hexxit.jar nogui

Increase the PermSize for bulky mods. With MCP in there, too, you may need to set the max higher than 256M.