Going back to what SuddenlyBRAINS said, I found a much easier way to get in the bank room in the Dalaran Underbelly. Using my method, you do not need to try and get lucky with getting your flying mount in long enough, or try finding the right kind of Underbelly Elixir. Read on, and you'll find out how.
1st - Go near the bank area in the Underbelly by the sewer exit where you can get on your flying mount. Look for some boxes.
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2nd - Start jumping up the boxes until you reach the last one. Mount up.
Then, get a running start and jump to that little ledge under the roof that should be right in front of you. You will probably land on it, and then you can just walk up the ledge onto the roof.
Then, go to the corner on the right side, and do the good ol' mammoth in the corner trick.
Start jumping on your mammoth and walking forward simultaneously. Once you start seeing through the wall, you know your almost there.
A few more jumps, and you should be good.
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And there you are.
Using my method, (as I said before,) you do not have to try numerous times with a flying mount, or spend God knows how long trying to find the Underbelly elixirs. This way, you can get it instantaneously.
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