Why am I smiling? This is what trigger-happy looks like!

Introduction

Hello and welcome to my very first guide to sniper.
Since I like to polish stuff for long time, this guide will be very raw but soon upgraded.
I'll try to keep it as simple as possible.

Pros / Cons

+ Farmed = win.
+ Easy to handle.
+ Not that mana-reliable.
+ Long range -> rarely focused first.
+ Very funny ultimate.
+ Silenced doesn't mean dead.
+ Relatively easy to keep very good k/d ratio.

- Low hp
- Absolutely no escape mechanism without items
- Farm reliable
- Stunned = dead.

Items

Starter

Nothing special, you need to stay in line for as long as possible.
Optionally, you can go into full-tango mode.

Early

Boots of speed - standard item for pretty much every one, useful if ganked.

Gloves of Haste - some cheap AS, can lead both to Power Treads and Hand of Midas.

FARM

Hand of Midas requires some explanation.

You need to farm yourself 1400 gold in order to buy it.

One can say: it is A LOT. You can go for half literally third that price right to PT and have same attack speed, bonus attribute and minor speed bonus.

Okay. Let's do some math.
You are collecting that 1400.
You gain just as much as in PT.
Cooldown is 100 seconds (let's say it is 110).
You gain 190 gold PLUS priceless experience. (let's say it is 155, you would have earned some of that gold anyway)
Let's say you gain it in 13 minute (average in my sample)
Average match takes 35-50 minutes. (let's say it is 45)
So you gain ((((45-13)*60)/110)*155)-1400=1300 gold with really careful math... + free experience and attack speed. Is this much? Well, farming became much more efficient, and the investment gives juicy, clean profit after about 11 minutes. So YES.

Core

Morbid Mask - allows you to stay in line for very long time, heavy harras including.
What is more important, it allows you to farm in jungle as much as you want.

Shadow Blade - core of a core, gives my favorite escape mechanism in game, some AS, some damage, and bonus first-hit dmg (often gives ridiculous amount of fun)
Instructions?
Ganked? Shadow Blade.
Focused? Shadow Blade.
Hooked? SHADOW BLADE + run in directly opposite direction Pudge would have expected
Stunned? SHADOW BLADE!
Low hp? Shadow Blade.
Need to run? Shadow Blade.

Generally at this point you don't have to stand cowardly in one line, time for some kill-efficiency.

Power Treads - Cheap AS + agility/strength (with HoM it literally comes in minute or two)

Crystalys - combined crit + headshot = annoyed (and often dead) enemy.
You can go solo Rosh at this point. Just for fun. ;)

Late

Daedelus - bigger Crystalys, allows you to kill literally everyone if given few seconds.
Works well with lifesteal.

Satanic - Massive lifesteal + big amount of HP (thus recommending Reaver first) + minor damage and armor.

Situational luxury

Aegis - pretty self-explaining item. Generally do NOT take it, but if you feel like destroying enemy's fountain, than.. why not?

Assault Cuirass - are you a teamplayer? this is something for you. Some bonus armor is never ever bad, and big AS bonus allows you to be not only a Sniper, but also a Sniper with Automated Sniper Rifle (with lifesteal)

Butterfly - very nice item when you are fed. Everything what is crucial for Sniper is here: Agility, AS, DMG. And 1/3 evasion. Perfect for pissing Drow Ranger, when she desperately tries to slow you with arrows and she misses 5 times in a row. Thus gives survivability.

Eye of Skadi - Ever wanted to be a Viper with big range? Now it is time for your dream to come true

Maelstorm - chain damage that stacks with lifesteal? Why not!

Manta Style - gives all around stats + illusions. I personally don't love that item as much as others do, because damage will be not that great, and illusions will be squishy. Although I admit, it is sometimes able to save your three letters.

Monkey King Bar - enemy Drow Ranger thinks that she is clever because she has Butterfly? Well. Not anymore. More Bash comes almost free of charge.

Mjollnir - biggest AS bonus in single item + static shield. If you played too much Call of Duty, and now love automated assault rifles this is something for you.

Shiva's Guard - again, very supporting item. use it when you want to safe your team from overpowered Lifestealer or Ursa.

Heart of Tarrasque - gives insane life regeneration and great HP boost. Ever wanted to be tanky sniper? Ho Heart + Satanic - funny time guaranteed. It isn't really THAT needed though, since with maxed Take Aim you can pick off towers, and they won't even shoot you.

Last, but not least:

Boots of Travel - they allow you to run from almost any gank, you die only when death-stunned. I usually buy them right after Satanic.

Alternative items.

Mask of Madness - pick it if you need more fire rate, and better escape mechanism.
Do not use it when you can be stunned - you are even more likely to be dead. Pick instead of Satanic.

Desolator - gives much bigger dmg output, but is conflicting with lifesteal, so personally I don't like it. Works much better with Bottle though - pick instead of lifesteal, obviously.

Bottle - Supporting item, very reliable when you need to use runes later. Small trick - you can use all bottle charges before taking rune - you will have full bottle again free of charge.

Do you like goose bumps?

I DO.

One and only...

Divine Rapier - when you want to kill everyone with 2 shots. Use with care. Although generally when you buy it, you don't have to worry about almost anything.

Skills

Shrapnel - Good for pushing towers, and pretty much that's it. However it is often useful to slow your enemies and/or safe your teammates. Hardest skill to put in skill tree. I am often skipping that skill to max stats ASAP. If you don't want to waste mana it is often best option. Generally it is worth to put at least 1 SP into this ability just to scare enemy team - at lvl 10. You have to find best option yourself.

Headshot - random bonus damage machine. Putting 2 points fast - jump is relatively big 15->45. Use for harass at early game and kill later.

Take aim - IMO most important skill in Sniper - gives you enough range to keep in safe distance both in lane phase and in teamfights. Max it ASAP. With this skill maxed, you can shoot towers and they won't be able to shoot you back.

Assasinate - ultimate trolling machine. Riki thinks that he is safe after killing 3 in row with 300 hp? Nope. Weaver walks into river with low hp, ready to buy expensive stuff into ss? Nope. Generally use it if your target has less then 1 bar of HP on 1st lvl, and less then 2 on 3rd lvl, and is running back to base. Don't be afraid of using it in not-100% kills. Often free frag, always more space for you and your teammates.

Creeping / Jungling

First of all: block creeps in your lane. It's a bit hard, but doable. Try to last hit EVERY single creep in your lane (prefferably middle). TRY to deny every single of your creeps. Generally I can even advise to hit your creeps all the time and only last hit enemy's - this way you can have line pushed to your tower and thus, be relatively safe.

Levels 1-6?
Stay in your lane.
Take minimal possible damage.
Do you see river?
That is lava.

DON'T WALK INTO ******* LAVA!

Team Work

As said before: finish running frags with ulti.
Keep your distance.
Deal damage. A lot.
Don't be afraid of runes. They can safe both you and your team.
But, most importantly: STAY ALIVE.
This is pretty much it.

Summary

Well. Hope you enjoyed this guide. As said before, I will polish it later (talking about fancy colors, links etc.) All comments and feedback will be appreciated. Oh, and please tell me if make any grammar errors, something like this could happen. ;)
That's all for today, folks.