Perhaps Icefrog and his tester think Shadow Demon is viable, and maybe he is, at least theorically, but nobody plays him.

Yeah, he can purge and slow people thru magic immunity on late game. WAOW!

I think if his kit is just too unrewarding to use. No burst, no flash farming, no escape machanism, squishy. Soul Catcher is nice, but a creep nearby can mess up with it and you need LOTS of damage on your side to make up for the fact Shadow Demon himself will not be doing much.

Doesn't help his disable is not easy to use and can mess up a gank as easily as it can help making it.

I'm unsure if the 0.25 cooldown reduction (from 2.75 to 2.5) on Shadow Poison will solve his problem.

Meanwhile, a hero who is picked a lot like Undying get a super sweet Scepter buff.

The frog works in mysteirous ways..