Rhasta - The Shadow Shaman, DotA Hero Strategy Guide

Rhasta is a very flexible and versatile hero. He is the only natural pusher, support caster and hero killer all rolled into one malnourished frame. The best disabler in the whole game of dota. But, you'll be needing to hone your ward trapping skills to use him efficiently.

-Hero Wiki-

Rhasta - The Shadow Shaman
Range: 550 | Move Speed: 285
Primary: INT
Str: 16 + 1.6 | Agi: 16 + 1.6 | Int: 21 + 3
Damage: 42 – 49 | HP: 454 | Mana: 273
HP Regen: 0.73 | Mana Regen: 0.85
Attack Speed: 1.43 | Armor: 1

Forked Lightning Calls forth a cone of lightning, hitting multiple enemy units for damage. Level 1 95 - 75 damage to 3 targets. Level 2 105 - 150 damage to 4 targets. Level 3 135 - 225 damage to 5 targets. Level 4 160 - 300 damage to 7 targets.

Voodoo Transforms an enemy unit into a random critter, disabling special abilities. Level 1 110 - Lasts 1 seconds. Level 2 140 - Lasts 2 seconds. Level 3 170 - Lasts 3 seconds. Level 4 200 - Lasts 4 seconds.

Hero Shackles Magically binds a target enemy, so that it cannot move or attack and deals 40 damage per second. Level 1 110 - Lasts 2.5 seconds. Level 2 130 - Lasts 3.25 seconds. Level 3 155 - Lasts 4 seconds. Level 4 185 - Lasts 4.75 seconds.

Mass Serpent Ward Summons 8 immobile serpentine ward to attack enemies. The ward is immune to magic. Level 1 200 - Deals 43 max damage. Level 2 350 - Deals 58 max damage. Level 3 610 - Deals 73 max damage.

-Skill and Item Build-

Forked Lightning is maxed out ASAP, as Shackles costs a lot early, and the extra milliseconds of disable do not matter as much as +75 damage.
Voodoo is taken only at level 9 and then maxed. It costs too much mana early. Ultimate is taken whenever possible.

Point Booster gives plenty of survivability, which is essential for Rhasta. It is much better than having four Bracers, as they consume a lot of space.

HoD is got versus heavy damage nukers. Blink is taken if you've problems with placing Serpent Wards and/or Shackles. As Keritzel and totalnewbie pointed, the nerfed Blink has very limited uses, for escaping isn't an option.

Book and Guinsoo's both give you great stats and active abilities. If you need a fourth () disable after Eul's go for Guinsoo's. If the enemy has many heroes with invisiblity and/or no one in your team is getting Book, go for it. This also gives you something to do during Shackles.

Luxury - Aghanim's and Heart.

--- Strategy ---

General

Laneing - Never solo. Ever. Rhasta is an Early to mid-game hero, and not laning with an ally totally wastes 40% of his potential. I recommend you lane with a high damage dealing spell caster. Perhaps the best lane partner for you is the Juggernaut. Have him start of with a pack of Tangoes and Boots of Speed. Shackle + Fury + Forked Lightning, and a kill is almost assured.
Forked Lightning is to be used only as a finisher if your ally can't finish of the enemy. Do not spam it, you don't have the Mana.

Ganking/protecting allies - Roam around the map in search of enemy heroes with a couple of mates to grab plenty of kills (ways to do this are discussed later). Remember, your role early is to gank a lot, while leaving the team carry to farm. Do whatever you can to save the carry, including Shackling the enemy so as to let the carry escape.

Usage of Spells

Forked Lightning - This has a casting range of 600, but it can extend upto 800. Aim for a hostile unit closer to you than the target if the target is far away.

Shackles - Do not use this if the enemy creeps are attacking you. You are more likely to die than your target if this happens. Timing is key here. Capture heroes once most of the enemy disables and ministun spells have been used up.

Voodoo - Target the biggest threat to your team. Sometimes it would be wise to Voodoo a disabler and then Shackle your main target.

Mass Serpent Wards - Warding and immediately Shackling is no brainer. Once you do this, double click a Ward and order the group to attack your target.
Wards can also be used to block of escape routes. They can also block enemies from getting at you while escaping.

Ward Trapping - This tactic involves some skill to pull of correctly. Basically, Blink (if applicable) up to the enemy and use Voodoo. Cyclone him and place Wards directly beneath the Cyclone (when the AoE selector turns red at the center). Now place them and wait for the enemy to fall in. Once they do, Shackle them immediately.
This can be done without Cyclone, just with Voodoo, but it is difficult and should not be your top priority.

Eul's Scepter of Divinity - Used for Ward Trapping, and to catch up with enemies.

Blink Dagger - Needed to Ward and/or Shackle effectively, as both the spells have a ridiculously low casting range.

Necronomicon - Summon before you Shackle the target. Proceed to destroy your helpless targets with your minions.

Guinsoo's Scythe of Vyse - Refer to Voodoo.