Sweet jesus. This can't turn out well for them.

"Well, I must say I'm impressed. I can't imagine how useful that would be." Rainbow just seemed to shrug it off.

"I guess that's cool, but why couldn't you make something that would make pagasi fly faster...um not that I need you to or anything." Twilight was ecstatic either way.

Few things here:
Pegasi, not pagasi, space after the ... , capitalize the Um, add a comma, that doesn't seem at all like a Rainbow Dash thing to say (seems like a Fluttershy character thing to say.) And the sentence structure is odd. The first bit makes it out to be Rainbow talking, despite it being Applejack. And if it were Rainbow speaking, it doesn't seem to make sense considering she "shrugged it off".

Rainbow just seemed to shrug it off "Well, I guess that's pretty cool. Still, why couldn't you make something that makes pegasi fly faster? Not that I need you to, just seems more useful."

That's how I would have put it, but it's just me. Again with the strange sentence structure, it appears to be Twilight talking despite knowing it is Rainbow Dash.
Also, my fears about this fic were validated in the first few paragraphs, sadly enough. Sorry, I can't read past this because I'm already terribly bored of the story. You could do well with a prereader, or at least look over your story a bit harder and maybe a second time next time. You have a lot of potential, but this isn't the best story to start with. Congrats on the feature box I suppose, farther than my stories have ever gotten.
I'm not trying to insult you if it seems that way, I honestly want to see you improve.

A very creative and entertaining Crossover. Really enjoyed every bit of it and hope to see more of your work in the future.

I LOVED it!!!! Cant wait to read more!

Welp imma guess (comments before reading chp. 2 ) that twilight teleports to georgia and gets wrapped up in all of this. Just a guess.

Well then....... seems fine.

Already mentioned this, but figured I would point it out.

"We got what looks like a...10-91..." The officer talked over it.

"I followed your case a bit, you bein' a Macon boy an' all." Now Lee was intrigued.

"You're from Macon then?"

"Alright. Oh! By the way, I figured out what I want to be for Nightmare Night this year!" Twilight stopped at the door leading downstairs.

"And what's that?"

"Instead of a dragon, this year I'm gonna be...a ZOMBIE dragon!" Twilight gave a wry smile.

"That sounds fun, but Nightmare Night is only a few months away, you might want to get started on that costume." Spike gave a goofy grin.

Oh, and not necessarily an error, but I'd recommend ditching Luna's olden speech. It popped up randomly in the chapter, and it doesn't fit. Her speech can be a pain in the ass and it's easy to mess up, I'd recommend just saying "she adapted" rather than try.
Again, not necessarily an error but it doesn't make sense as I don't think he started addressing them as Walkers until later on. "The Monster" and "The Creature" works just fine.

On a side note, I noticed the changes you made and I approve. You improved. Your spelling seems fine, but I did skim through.

After the cuffs were succesfully removed, Lee rubbed his aching wrists in relief.

I missed another one apparently.

'Focus..._just a simple teleportation spell...' Twilight thought to herself.

Capitalize the start of your sentences.

Okay, seems like you have the exact same problem as the majority or writers on this site; making paragraphs. Here's the thing: cutting them exactly at each spoken line is just one flimsy step above walls of text.
Here:

"Oh, landsakes. Do you never stop goin' on about joinin' those guys." AJ jabbed. Twilight was still ecstatic either way.

"Oh, I can't wait! It's not quite finished, but I still want you guys to come see it!" The ponies looked at each other and shrugged.

"We'd love to see it Twi."

"Meh, I ain't got nothing better to do." Dash shrugged. Twilight hopped in the air.

Can you see how the colored text is all mixed up? Each is a different perspective, a distinct point of view. By only paragraphing with each spoken line, you're cutting the vast majority of them in half and tying up the wrong ends.
Now look:

"Oh, landsakes. Do you never stop goin' on about joinin' those guys." AJ jabbed.

Twilight was still ecstatic either way. "Oh, I can't wait! It's not quite finished, but I still want you guys to come see it!"

The ponies looked at each other and shrugged.

"We'd love to see it Twi."

"Meh, I ain't got nothing better to do." Dash shrugged.

Twilight hopped in the air.

Doesn't it look all that much better when each character's actions AND lines are all bunched together? Doesn't it make the read flow more smoothly?

I'm loosing this cross over so far. the detail and description of the scenario is really great :D must read more!

Raven: Could've been better, frankly, but still good.

Dr. X: I am worried about where Miss Sparkle, Rainbow Dash and Applejack teleported......

Raven: ....... Now, that's a good question. Hope they didn't teleport right in the middle of the zombies.... And why do they use the term "Walkers" instead of "Zombies"???

3355143 In the Walking Dead verse the idea of zombies never existed- it isn't ingrained in their culture at all.

I just wanted to thank you. The whole reason I'm into the walking dead game was because i stumbled across this fic. THANKS!!!!!!!!!!

OH MY GOD I LOVE THIS FIC!!!!!
IT IS SOO AWSOME
all the feels
keep up the good work bro you are awesome
oh btw when are the next chappters out? :D

... brings up sad memories this LONG LIVE LEE!

holy crap! this is actually pretty good!

Bravo!

5136731 rest in peace lee

Oh, this will be fun.
And interesting. Nice job on this so far, a few mistakes but nothing too bad.

Good job.

FINALLY!! A Walking Dead Game cross Mlp. I'VE BEEN SEARCHING FOR SOMETHING LIKE THIS FOR AGES!!

"Thank you, Luna. I will make sure that none of this gets out of hoof."

Now I'm wondering if this zombie outbreak is galaxy spreading.

Or that if the Main 6 arrive on Earth, they then become infected even without dying, and head back to Equestria.

If a single pony dies............Equestria might be doomed.