65-70% winrates with Storm, Necro, and Leshrac. All over 100 wins. 4.4k mmr.
Storm: Start with null talisman unless the enemy mid is going to be spamming spells, then just get a wand. You can pretty much watch Blitz to figure out how to play him. The only things I haven't seen him mention is that Euls is a really good item to counter silences. You can kill pretty much any enemy mid at level 6, so take advantage of it. Just make sure to hit all of your overload charges.
Necro: I always go null talisman into dagon, blink, aghanims, ethereal blade. People at my mmr always bitch that I'm not going Mek, but fuck them. With dagon 1 and level 7, you can instantly burst a hero with about 700 health. If they have more than that, you can just auto attack a couple of times to get them down. Level 1 ult is crap, so don't rely on it. The biggest thing for him is to just always be looking for pickoffs. Also, the combo is ult -> ethereal blade -> Q -> dagon. If you don't ult first, you'll give them time to wand or BKB or something.
Leshrac: Mostly from YEARS ago, but the only real difference between how I played him then and how I play him now is that his lightning is actually useful. At the start of the game, what you want to do is keep the enemy low with auto attacks and the occasional lightning (try to use it to get last hits and hit the enemy hero so you kill two birds with one stone), and then when they're low enough, you lightning -> stun (it'll be easier since they're slowed) -> auto attacks/another lightning. You can pretty much kill any other hero 1v1 at level 2 just through lightning spam and auto attacks then using your combo. Build is bloodstone, euls, octarine core, BKB, boots of travel. Not necessarily in that order. Bloodstone/euls first though, octarine/boots after that. BKB depending on the enemy lineup.
I also have a 66% winrate with shadow fiend, but I don't know how I do it. I usually play him by starting jungle at level 1, then winning only because I have better map awareness than anyone on the enemy team