At the moment, out of all of the current top tier items in Dota 2, Shadow Blade is by far one of the most popular simply because it is considered to be a universal buffer. This means that it is actually good for every character, not just one or two, as is the case with most other items.
But, even so, you still have to take into consideration the fact that while it is great for everybody, it is specifically amazing for these following characters, for the following reasons:
While it is true that magical damage is very important for Shadow Fiend, what people don’t realize is the fact that this hero’s right click potential is just as amazing. Because of this, we recommend using the item if you want to turn your SF into a super-fast mid lane farmer.
You will be able to become invisible with it and before long you will be able to gank and escape any situation whatsoever.
Spirit Breaker is a must have for any pro team out there, and that is all thanks to his pub stomper abilities. He can easily charge through the towers and take everyone down, which is why he makes for a great teammate for other mid-laners like Queen of Pain for example.
Shadow Blade is great for him because it helps turn him into a tank. Sadly, he is not a fast farmer so it will be hard for you to actually get any hero kills during the beginning of the game.
Slark is already known as one of the most annoying heroes to match up against in Dota 2, which is why Shadow Blade makes for such a great addition to his arsenal. It turns an already hard to beat enemy into a tank that can easily escape any damage whatsoever without even having to use his ultimate.
On top of that, using both his ult and SB at the same time will give you even more movement speed and it will make your HP regeneration insane.
Sniper is a glass cannon type of a character, meaning that while he can definitely do a ton of damage, he is also very easy to take down. This is why people invest into items such as Butterfly, Monkey King Bar and whatnot for him.
But Shadow Blade is also very good for him especially if you eventually update it to the Silver Edge item.
Yet another glass cannon type of a character over here, you can also use Shadow Blade on this hero to make him feared all across the field. The main difference between him and Sniper is in the fact that Drow Ranger is usually the carry, while Sniper most often takes the mid-lane instead.
While most players would quickly pick Blink Dagger for Legion Commander, you should also invest into Shadow Blade for him because it gives him that extra bit of damage that he needs to be a real menace in game.