Hello! This is just a quick build along with my reasons for using each talent.
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Sylvanas is a very powerful hero right now. She has great escape, chase, and is the single most dangerous hero to leave alone in a lane, able to level cannons and keeps in no time.

Barbed Shot:
This talent allows Sylvanas to constantly have a minion advantage in lane, keeping enemy heroes pushed back. As soon as mercenaries spawn, she can more quickly dispatch siege camps solo, and bruiser camps with 1 other hero.
It also has synergy with Splinter Shot.

Envenom:
It seems out of place, maybe a little?? It really is not, however. Envenom gives you the additional edge needed in ganking, and pressure in lane. When paired with Shadow Dagger, and Withering Strike, you will have all but the tankiest heroes running for a well. It makes Sylvanas much more useful overall.

Life Drain:
This is an amazing sustain talent. Sylvanas is fairly squishy, and has little as far as sustain is concerned. This allows her to stay alive, and continue to push lanes, and pressure heroes, healing any damage you might have received while pushing hard into their keeps.

Wailing Arrow:
You will be clearing enemy minions, not stealing them with Possession. Your ability to kill enemy minions and mercenaries will far out weigh stealing one and buffing it slightly. An AOE Silence is extremely useful in team fights, and amazing for shutting down enemy 'tide-turning' ults such as: Malfurion's Tranquility, Lili's 1,000 Jugs, E.T.C.'s Mosh Pit, and several others. Along with the silence it deals a decent amount of damage on top of it. All around a much better choice of an Ult, in almost any build.

Splinter Shot:
This talent has synergy with Barbed Shot, taking this talent allows you to clear MASSIVE groups of minions in a matter of seconds. It is great in team fights for additional pressure and damage, along with making solo bruiser camps very quick and easy.

Cold Embrace:
What an amazing talent for team fights/ganks/minion clearing. Shadow Dagger a minion that is part of a massive group pushing one of your lanes, combined with Splinter and Barbed shot, every minion will be gone in moments not seconds. This talent has great gank potential, and is easily spread if enemy heroes are near buildings/minions. During team fights, your Shadow Dagger will spread to each member of the team, making them all take 25% extra damage from your team's attacks.

Bolt of the storm:
The Deafening Blast is great for longer silence, but it is only for inner targets, not the entire AOE, and the increased damage is merely okay, and also restricted to inner targets. The survivability and use of this skill trumps the other uses. You have one decent escape, but it is slow and not always useful when you have 1 direction. This gives you the needed escape, or needed chase leverage to ensure that you live in shady situations, and kill the enemy when all he needs is simply 1 more Withering Fire bolt.