Valkyrie

Skill Build
1 – Courageous Leap
2 – Javelin of Light
3 – Call of the Valkyrie
4 – Call of the Valkyrie
5 – Call of the Valkyrie
6 – Javelin of Light
7 – Call of the Valkyrie
8 -Javelin of Light
9 – Javelin of Light
10 – Valkyrie’s Prism
11 – Valkyrie’s Prism
12 – Courageous Leap
13 – Courageous Leap
14 – Courageous Leap
15 – Stats
16 – Valkyrie’s Prism
17 – Stats+

Justification / Modifications:
Get Javelin of Light first (Leap second) if you plan to rune-gank. It’s probably the strongest rune-ganking skill in the game.
If you start pushing before level 10, get Valkyrie’s Prism earlier.

Lane Starting Items:
2x Runes of the Blight, 2x Duck Boots, 2x Minor Totem

Core:
Bottle >> Marchers >> Power Supply >> Steam Boots >> 1-2x Soulscream Ring

Ghost Marchers are viable too, as positioning is very important for her. Also you should be able to quickly close in after an arrow. Ghost Marchers favor ganking while Steam Boots favor carrying.
The easier the game the fewer Rings you will need.

After Core:
(Nullfire Blade >>) Frostburn >> Charged Hammer >> Riftshards >> Symbol of Rage

Get a Nullfire ASAP if your team needs to counter Hellbringer, Hammerstorm or Jeraziah. Otherwise go for the listed semi-carry/carry build.

Information
Roles: (Semi-)Carry, Ganker, Initiator
Prefered Lane: Any. Can solo Mid, or side preferably paired with another disabler
Difficulty: 4 – Hard (Arrows…)
Farming capabilities: 3 – Decent (Call helps a lot)
Item dependancy: 4 – Heavy
Power:
– Early Game / Lane Control: 3 – Medium (very dangerous arrow stuns, heavy nuke)
– Mid Game / Ganks: 4 – Strong (Extremely Strong Ganker, can control the game from mid lane)
– Late Game / Team Fights: 3 – Medium (Can be 4 – Strong if she dominated the midgame, her ultimate is amongst the best initiation)

30-Seconds-Guide:
– If you have problems hitting your Javelin, wait for someone else on your team to cast a disable, then throw the Javelin at the non-moving target.
– Valkyrie’s Prism is a very strong initiation, escape and counter-gank tool. But the Priority is on initiation, especially if you are lacking other good sources of it.
– Use Call of the Valkyrie (once it’s level 3+) to punish enemy melee heroes if they go in melee range of the creep waves.
– Especially if you play in mid: Gank a lot!

Counters:
– Valkyrie is VERY hard to counter. 2 Escape Spells, high physical and magic damage, long range/duration disable. Hero-wise the best counters are stunners and disablers.
– Item-wise i suggest you carry Dust. Don’t bother with armor or anything like that, it will not help much.
– Even when heavily farmed a Valk is still relatively squishy. The best counter is to focus her when possible.