Eats Shoots and Leaves

Totally don't get your starting items. Why would you need the stick that early? Especially when you don't spend any mana at all. Also having no Salve as Sniper can invite people to harass the **** out of you early.
Morbid Mask isn't really good, only to farm neutrals maybe. Mask of Madness can be legit though. Second Mjollnir is a bad recommandation, you should rather get MKB or Deso or Manta.
Don't underestimate Shrapnell. I get why you don't skill it early, but after lvl 16-18 you should be skilling it to pressure Tier 3 Towers etc.

Thanks for your comments / questions.

The stick is in there early for a couple of reasons, but you could leave it out if that is your preference. For one thing, if someone is using abilities to harass you, then the stick helps to mitigate that by providing some health. Second, it can provide that health boost as you're running away and even taking damage, unlike other healing options available at that juncture. Lastly, having it early means that it is gaining charges that will carry over when it gets upgraded to Magic Wand. Again, those charges are nice to have as a quick HP reserve if things hit the fan.

Morbid Mask is great for farming neutrals, which is why I specifically noted it in that way. Again, it's optional. Mask of Madness strikes me as a poor choice for Sniper due to his squishiness.

By the time that a second Mjollnir would be an option, like I already noted, get whatever suits you. I think it's a fine option under the right circumstances, but that decision comes after what is covered in this build -- the purpose of which is to get a fast-firing, reasonably hard-hitting sniper with the ability to get out of the mix when needed.

Regarding Shrapnel, I'm not underestimating it (or estimating it at all). It simply serves no purpose in this build. The mana pool is used purely for Assassinate and Shadow Walk, and the earlier stats are more valuable to Sniper in this build since they increase his survivability and make him hit harder and faster. Also, since Sniper can outrange towers with his autoattack, he doesn't need Shrapnel in order to push (by the end of the build).

Oh, I almost forgot to address the comment regarding Healing Salve. I personally don't care for it, since I can get a 3-pack of Tangoes for a lower cost, and the Tangoes still work if I take damage, unlike Healing Salve. Also, with Healing Salve, you either have to waste a bunch of it, or you have to wait until you're almost dead before using it. The Tangoes let you heal at a much earlier juncture.

I would only get a Magic Stick starting if I was laning against a Zeus or maybe a Shadow Fiend. Also, you need to add Desolater and [Manta Style]]. Add some color too, but otherwise, decent guide. :)

shrapnel does 14dmg per second to towers at its highest level. take aim means you can sit out of the towers range and tear it down

I did a quick test at Sniper level 16 with Magic Wand, Power Treads (agility), Shadow Blade, and Mjollnir. It took ~20s to take out a tier 1 tower. With a second Mjollnir, it took ~12s. With an Abyssal Blade instead of the second Mjollnir, it took ~10s. Either choice is perfectly viable, depending on whether you want to focus on even more attack speed or damage in the end.

Items and abilities tagged so that icons and links show up.

Here's an example of the build in action.

You don't have to start with Magic Stick. Get it later?

Fun Fact: Salvos have a slightly better HP:Gold ratio than tangoes.
400 hp for 100 g = 4 hp/g. 115 per tango x 3 - 345 for a stack for 90 g ~ 3.83 hp/g.

Finally, you might want to add a Manta Style in there. It gives a total of 50% increased DPS.