This is the pure carry guide to Sniper. This build focuses on maximizing farming and survivability first, then damage later. With this build, you may find yourself with more assists than kills early game, but if you stick to your farming game, you'll carry your whole team to victory.
Skill Build Explanation
Assassinate > Take Aim > Head Shot > Stats > Shrapnel
It's my personal taste that this skill is an unnecessary drain on your mana, which should be saved exclusively for Assassinate. Shrapel also is an unnecessary drain from your skill points.
One of the best damage dealing skills in the whole game, yet it has only 20 second cooldown. Many people who play snipers use this only as a finishing move, but Assassinate is one of the best harassing skills ever. Don't forget to spam this skill, which usually will push the enemy heroes back, giving you a lot of space and time to farm. If they don't go back, you just have to patiently wait 20 seconds to shoot again (given you didnt waste any mana on shrapnel)
Increases your shooting range. Sniper has an almost-instant shooting animation, and with Take Aim maxed early, it's extremely easy to last hit. Also, remember that Sniper is very fragile. The longer your shooting range is, the safer you are. The longer your range also means the more shots you can pull off before the enemy is out of sight. A level in Take Aim adds much more practical damage than a level in Head Shot.
The ministun is very useful, but do not rely on the extra damage from this skill. Get crystalis and Head Shot will start to shine. It's the mini stun that will make all the difference in mid and late game. Get Take Aim first.
Item Build Explanation
All starting items are optional and flexible, as long as you get at least 1 tango and some items that will build up to Wraith Bands later.
Early Core Items:
Sniper has only 3 ways to deal damage: Shrapnel, Assassinate, and normal attack. Given that we completely disregard shrapnel to save mana for spamming assassinate, we need to buff up our normal attack as soon as possible. That's why 2 Wraith Bands are taken, because they buff up Sniper in all aspects.
Your next item to build is Crystalys (which buffs up sniper's normal attack seriously, while working in conjunction with headshot). Since Crystalys take a while to build, you should get a morbid mask somewhere in the middle of building it. Morbid mask makes jungle farming a breeze, and allows you to heal just by nonchalantly shooting at creeps from afar. Morbid Mask is extremely essential because it saves you trips to the fountain. Many times i find myself to be the only player with maxed health in the middle of a team battle, and that is the direct result of Crystalys + Morbid Mask
Late Core Items:
We're simply moving onto the stronger version of of Crystalys + Morbid Mask, which is Daedalus + Helm of Dominator. If you're constantly farming, you should complete this set by roughly level 15 - 17.
After Core Items:
You can go for butterfly if the enemy has a carry that can still fight face to face with you. My favorite is Satanic though. As long as you're not stunned or disarmed, Satanic can give you 4 seconds of near invulnerability, given that you keep shooting and given that you have Daedalus. I've singlehandedly won many 1 v 2 or even 1 v 3 fights with this.