I told you to go right

When I got back up, I was on the floor. I couldn't remember why. I was also in a cave. I couldn't remember why. I stood up, and glanced around the place. It was dark, but I knew the place already. I just couldn't remember why I was there. So, I began to trot towards the old rail-tracks nearby, and follow them upwards. If I remembered correctly, it would lead me to a small alcove, with a hidden lever. Inside, I could nick a lantern and some form of weapon, pull the lever, and head down the tunnels to the throne room. There, I could try piecing together why I was down the tunnels.
After a while of following the rails, with nothing but the low whistling through the tunnels to keep me company, it began to head down again, the correct path to the alcove. Smirking, I rested both hooves on each side onto their respective rails, shifted forward, and let my horseshoes slide me down the rails. It was the most fun I'd had since I lost my wings, and not to mention the fastest I'd ever been going since I got out of bed with Luna that one morning.
When I reached an estimated speed of 90MPH, the alcove came into view. It had a door leading to unimportant places, boxes of equipment, lanterns, and a suspicious lever on the wall. Smiling, I jumped off the rails, landed on my face, and slid on my face until I ran into a box.
"Painful..." I muttered, picking myself up and dusting myself off. I wasn't sure what the green stuff was, but it probably wasn't important. Instead, I focussed on finding a weapon, so I rifled through a few crates. "Pickaxe...femur bone...piece of rock...crowbar. Crowbar?" I murmured, picking the iron rod up and giving it a few swings. It had rust all over it, black ends, and a red centre. "Familiar crowbar." I grinned. With that held in my hoof, I pulled a lantern from a wall with my mouth and held it there, before tugging the lever on the wall.
Grrrrkkkkkkkkkkkkk...CHUNK.
As soon as it opened, I heard something stir down the hall.
SLAM.

Ok, not taking that route.

"Hello?"
Huh? Was that a voice?
"Is anypony there?"
Yeah, a voice. Better find it's owner.
"HELLOOOO!" I called out, putting the lantern on the floor.
"Oh thank goodness, somepony's there! Who is it?"
"THUNDER MUSTANG! AND YOU ARE?"
"Thunder?!?!" In the dark, I could see a mist moving closer towards me, attached to a figure that was larger than me. "Is that you?!"
"Luna?!" I called back excitedly. "Is that really you?!"
Yes, it's her. And me, as well.
What the-who are you?! G-Stallion?! I thought I told you to fuc-
No, it's me again. You know, the first pony who could be bothered to speak with you in your domain?
...Nightmare?
Oh, so now you remember me. You'd probably remember me better if I came up and pressed my flanks against your face. You're still interested in that, correct?
W-Well, I-I didn't know you could even e-exist. Y-Y'know, being defeated by the Elements, and all...
Oh, ignore that garbage, because we both know that nothing can break our bonds, hmm? And just so you know, I can cling onto a concious being and live alongside them in silence. And if you decided to try kicking me out, I don't believe you'd want my wrath, hmm? No, I didn't think so. As I was saying, I have returned in your servitude.
What?! Why?!
Well, mostly due to the fact that you kept me amused as your friends 'defeated' me, and partly because I can't control you, I decided there was nought else to do, but help you on your way. Unless, of course, you don't want my help...?
No, no, I'm grateful, Nightmare, I-I'm thankful you're willing to help. It's just: wouldn't Luna flip if she met you in here? Or, if it's still possible, out of here?
She said she was curious, correct?
Well...I can see where you're going with this...but yes, she did...?
Then we're sorted, love. After this wedding fiasco is over, and Luna is convinced to our 'cause', expect the rutting of your life, from me and your marefriend at once.
Christ, I'm actually hot for you again. Wow.
That happens. Now, you'll just need to know that 'Lulu' is having the same problem as you right now, and can't remember why she's down here. You'll need to tell her the way, so she can fly both of you out of here. Plus, if you can convince her, ask her if she could maybe give me my own body? I miss being able to walk and pleasure myself.
Alright, alright, I'll ask her. And Nightmare?
Yes, sweetie?
Welcome back to Casa del Thunder.