Riddle Me This

My house was a wreck, just like how the aftermath of a well-partied house normally looks like. But I was too exhausted to clean up. I just wanted to retire for the night.

I headed toward the kitchen, intent on brushing my teeth to remove all the excess soda, chips and gravy from my mouth. I had to pass my the dining area and noticed something that was very orange from my peripheral vision.

I did a double take. Walking backwards for three steps, I stared dumbfoundedly at the pumpkin on top of my dining table.

The way it was carved gave it a nasty look and malicious presence in contrast to the classical design of the room. I moved closer to inspect it, wondering which one of my crazy friends came up with this prank.

Positively surprised, I found a piece of paper tucked underneath the pumpkin.

I love riddles!

Forgetting my original plan for the night, I sat down and began solving the riddle.

"MY FIRST IS IN GIGGLE AND ALSO IN LAUGH,
MY SECOND IS IN THIRD AND IS ALSO IN HALF
MY THIRD IS IN HORROR AND ALSO IN BONE.
MY FOURTH IS IN SUN BUT NEVER IN MOON,
MY FIFTH IS IN CASTLE AND ALSO IN KNIGHIT,
MY WHOLE WALKS THROUGH WALLS TO GIVE PEOPLE A FRIGHT."

The first three lines were a piece of cake. Each of the pair of words, only had one similar letter: G, H, and O.

I rubbed my foot over the other, feeling the temperature drop. I already turned the heater on, so I thought it was odd. But I wanted to finish the short riddle first before checking.

So, the fourth line had two possible answers: letters U and S. But I gathered it was S in the figurative implication.  You, which may mean I or any human who reads this, can go to the moon.

I felt the hairs behind my neck stand up and goosebumps start to appear on my arms. It was so weird. Normally, the house isn't this cold even without the heater on.

I rubbed my palms against my arms to generate heat. For the fifth clue, there was Castle and Knight. They both had letter T.

Altogether, I got...

The lights suddenly went off.

Mumbling under my breath about the freezing temperature, I stood up to find a flashlight. I clicked it on and found my breath puffing out clouds of white air.

The flashlight slowly flickered off. I headed for the kitchen to find some fresh batteries, only to stop again.

In the darkness, the shape of the pumpkin's carvings were highlighted. But that wasn't what made me drop the flashlight.

The pumpkin was standing, freakishly lean and tall.

Smoke rose from its mouth as it spoke, "Riddle me this, do you know who I am?"

I knew the answer to the riddle, and then understood what the last line meant.

"Ghost..."

Then, it rushed forwards.