Temple Run 2 – How to Pass the Slip n Sled Objective: Proven Strategies

I believe, I have got the answer. The score multiplier go like this. When you upgrade it for the first time, it gives one multiplier. When you upgrade it second time, it gives two multipliers and so on. So 5 upgrades will give 15 multipliers in total.

It is basically a bug or an unfinished piece of code. From this thread you can see that many other people have it and one of the opinions is:

This is a bug, an error, in the game. A "miser run" is one in which you avoid collecting coins, but in this case no goal number has been set. "Desc" is short for for description. The programer placed this temporary text to remind himself (or someone else) to place description text for the miser run. In the original Temple Run game a Miser Run was running 500 meters without collecting any coins, so either this was simply a repeat performance it it was actually code that was copied over from the former game, but not completed. If you look in the main current objectives list you'll see that it does not show up. I was able to make this objective disappear by starting a run and simply running off the first ledge without jumping.

So don't worry about it, it's just there to take some free space. It might be updated in the future with new objectives(I hope)