"It's okay," Rainbow assured Twilight. "If we hurry, we can make it out." But even Rainbow didn't think that was true. She couldn't bend the mud, but even if she could, she was too weak to do so.
"Can't you curve the mud or something?!"
"No, I can't BEND it. I don't know why, but I can't bend mud. I can bend water, dirt, and rocks, but not mud."
"Are we almost there?", Twilight asked, frightened.
"Yes. It's getting harder to feel the vibrations, though. I can't feel them through mud. Only dirt and rock...Wait! Your horn! Can you push the mud away with a spell?"
"Uh, not exactly."
"What?! What do you MEAN, 'not exactly'?!"
"Most pegasi and earth ponies don't know this, but unicorns have weaknesses. Mine is mud. Even if a LIIIITTLE mud touches my horn, I won't be able to use it for at least three days."
Now it was Rainbow's turn to worry. The walls were still closing in, all made out of mud, and there was nothing she could do about it. For once in her life, she couldn't do anything. She felt useless.
"Rainbow?"
Rainbow tried to look at Twilight through all the mud, but it was nearly impossible. "Yes, Twilight?"
"Is this the end?"
"Twilight, don't say that!" Now both Twilight AND Rainbow were crying over the loud thunder. "We'll make it!"
"Rainbow, I just wanted you to know, you've been a really great friend! I'll never forget you!"
"You've been a great friend, too. If somepony were to take away my memory, I would never forget you!"
Rainbow and Twilight reached out, and touched each other's hooves. Not even the mud, rain, and dirt could separate their soaked hooves.
Rainbow took her last breath, and she guessed Twilight did the same. The mud devoured them.