This is the build I find the most useful for Valla. I have based it on league of legends characters {I am a LoL player} such as MF and Vayne. Lots of lifesteal, slow, and stun.

I was recently playing this build and some kids we're giving me a lot of sh*t about it. The purpose of this build is to murder the enemy team in close range and use her abilities to flee to safety. Since her Trait stacks, Valla is able to infiltrate enemy lines and apply massive amount of damage as the enemy runs as she hits them with tons basic attacks. If the enemy is to turn and fight however, Valla can use a Vault to retreat to safety and regain some health with some more auto attacks. I find that when playing Valla her Strafe ability doesn't do enough damage to enemies that are running away from the shots. I pick Rain of Vengeance because of the 2 stuns, the 200+dmg and the ability to upgrade that into 4 stuns and 500+dmg {that's per champion hit!}. This ability has proven critical in team fights and often is able to turn tables in the team fight.

Any questions or comments? I would love to hear feedback on this build.