Man, I forgot just how crazy Shadow Demon gets if he has a level advantage.
People keep taking him support these days, which is reasonable. He has good skills. But goddamn, he needs to go back to his original role. Mid lane. It's impossible to lose. Right from level 1 you'd basically do double damage to everybody. Autoattack, shadow poison, autoattack, shadow poison, repeat until dead. You don't have to duel till the end too, just do that about 4 times (should be about the same time your opponent realizes he's fucked) and press D.
All you need is one level in shadow poison and you're set. Then you max disruption. Followed by soul catcher, though you kinda want all three asap.
Jesus christ the damage from the combo.
You walk up, trap them in disruption. Then you go to town. Lay on the soul catcher on that ball. Then a shadow poison (ideally you want to have stacked one of these before you disrupted). By the time the guy comes out he's already dead.
Things I didn't realize way back when, and probably stuff most newbies wouldn't know:
1. The amount of DPS that the illusions do combined is 120% of the original hero. That's pretty crazy, and some amount of micro will be needed to get the illusions to attack the target instead of some random thing. It also stacks with his soul catcher.
2. Soul catcher only affects one target even though the AOE is so gigantic. Which is fair, considering it's like some kind of super Orchid. So what you want to do is get someone in disruption, then use soul catcher right at the edge of it so the guy inside disruption will always take the 50% bonus damage from EVERYTHING for 12 seconds. That guy is so boned.
3. Demonic purge is godly. The range on it is exactly the same as Shadow Demon's vision radius at night. So basically, if you can see a target, he can be ulted. This also does so much stuff it's bonkers. It gives a huge slow equivalent to Viper's ultimate. It also does good delayed damage (that works with your W). And best of all... you see that Dark Seer zooming away? Omniknight with Repel and Guardian Angel coming in? PURGE!!!! MWAHAHAHAHAHA!!! Cooldown is super short too.