The Scroll can be obtained by defeating Zabuza on the Great Bridge, if you defeat Haku as well, you can obtain the Ice Dragon Scroll, which can be found here.
Once used on a player, it can slow the player down and give the blurry effect, damaging them, you can use the first move of Shadow Release. And then use the Hidden Mist, since the first move of Shadow Release can damage the player, along with the Hidden Mist Scroll, it can probably be a guaranteed win once used along with Rashomon, it also takes only 35 Chakra once used.
People can easily escape unless you have a stunning technique like Water Prison or Wood Dragon. (And the first move of Shadow Release, which is Shadow Stitching.)
(WHEN BEING USED ON YOU)
When it is being used on you, one of your disadvantages are that you cannot walk as fast as you are slowed down, especially as to when people use a stunning technique like Shadow Stitching, the first move of Shadow Release, or Water Prison, and Wood Dragon. It is one of the worst Sub-Jutsu(s) to be caught in especially if your opponent has a good combo for it.
(PLS EDIT IF POSSIBLE)