Theory Crafting: Viper

Viper is a hero that is an excellent ganker and has some good survivability.

The Hero

Skills

1. Poison Attack: A cheap cast spell that provides an attack speed and move speed slow, as well as a bit of magic damage over time.
2. Nethertoxin: A passive spell that deals physical damage based on missing HP as well as adding some bonus base damage. It is less effective against creeps, dealing only 50% of the damage.
3. Corrosive Skin: Another passive spell that slows the move speed and attack speed of anyone attacking him while dealing magic damage over time for 3 seconds. It also adds some magic armor.
4. Viper Strike: A pretty big slow for 5.1 seconds that also deals pretty decent magic damage over that time. The cooldown is pretty short too (80/50/30 seconds). The only problem is it costs a lot of mana.

Traits

• Slow as hell starting move speed (285)
• Decent attack range (575)
• Kind of squishy early game

Current Meta

 He's not used frequently in pro games. At one point, Viper was sometimes picked up as a solo mid. Now, he's only seen much in match making.

Items are pretty standard carry stuff:

• Power Treads (survivability/adaptability)
• Vanguard (more survivability)
• Manta Style (move speed, DPS, survivability)
• BKB (survivability)

Usually, he's taken solo mid and ganks a lot because his slows are heavily geared towards being a ganker.

You'll typically see a Viper maxing out Poison Attack, Nethertoxin and Viper Strike first before taking Corrosive Skin.

Theory Crafting

 Build 1: Radiance Carrier

The idea here is to get some early farm, make a Radiance, and push lanes using the Radiance aura and Corrosive Skin. This is how I see it working:

1. Take Viper mid
2. Go with a skill build prioritizing Poison Attack/Nethertoxin
3. Get Phase Boots (or Tranquil Boots) quickly. Both give you the movespeed you need to roam and gank.
4. Get lots of kills and save for a Relic
5. Make Radiance and push lanes with it
6. Tank up a bit (BKB, Manta Style, Linkens, Pipe, Heart, etc.)
7. If you get the chance, upgrade your boots to Boots of Travel so you can move between lanes

Situational Items to Consider:

• Drum of Endurance: HP, Movespeed, Attack Speed, and Mana - pretty much all things you want
• Shadow Blade: Survivability and Ganking - in MM, most people will not counter you by getting wards and such. If they start buying detection, then they are spending money they wouldn't have needed to spend otherwise.
• Poor Man's Shield: Survivability and AGI - depending on your stating items, it might be an OK upgrade
• Aghanim's Scepter: If you're ganking a lot and could use the upgrade, it could be worth the money. Definitely adds some survivability.

Build 2: Jungle

The idea behind this one is to max Corrosive Skin first, get a Poor Man's Shield, and give someone a solo lane in the process. You can easily poke out of the jungle for a quick gank. This is how I imagine it:

Skills:

1. Corrosive Skin
2. Nethertoxin (to kill creeps faster)
3. Corrosive Skin/Poison Attack (depending on whether you want to set up a lvl 3 gank)
4. Poison Attack/Corrosive Skin (depending on whether you ganked or not)
5. Corrosive Skin/Poison Attack/Nethertoxin (depending on what you need)
6. Ult

Items:

• Poor Man's Shield: gives you AGI and blocking
• Tranquil Boots/Power Treads: Both are good, just a preferential thing

From there, it's sort of whatever you want to continue on to. Maybe the standard build? Maybe the theoretical build above (rush Radiance)?

My main concern with this build is that Viper would either not be tanky enough to jungle so early or not be able to farm fast enough.