Oh, my! This was enjoyable. It reminds me of those stories that flooded Fimfiction a little while ago, the first was Twilight Sparkle's Bathroom Is Flooded with Semen, or something like that. I won't read the spoiler note, so I'll be surprised to find out who or what the target will be.

6113112
I read those. I think Twilight's fury might've caused some wet metaphorical pants, at the end there. That was Hilarious Agreed?

6113343 I need to go find and read the whole set of those some time. I only read the first. It was hilarious, though. Scoot and Dash here have similar potential (of course, with a different spin).

Oh god... this prank, jesus XD This will be interesting... very much so.

Good job.

6113377
Awww.... Oh, well. I guess.

You definitely should. I still don't know how I found them, though. Sorry, cause that means I can't help ya. Which sucks big time. As in 'Macaroni Monkey-cake' and 'Whale-box Balloon' suck-level.

So far this is really good

She grinned again, knowing first hoof what that cloud was full of and the anticipation of adding to it again today...

No. You didn't just describe Dash as having-

Ah who am I kidding. You did.

 it was rare for somepony to allow another pony to mount them.

While it did occasionally happen, typically, it is reserved for a parent and child or very close special someponies; the latter was very much a private experience

Does this apply to dragon-riding-on-mare as well?
Twilight, you naughty mare~!

The filly fought down a blush and cleared her voice, forcing the excitement in her voice and body down before she finally spoke. “Of course Rainbow Dash. You know I would do anything for the coolest, most totally awesome fillyfriend ever!” She paused for a moment, her curiosity piqued as the question she had never considered before that moment came to mind. “So, um, what are we going to use this for anyway?”

To give each other nice hard squirts repeatedly!!!