This build is one that I've come up with on my own through playing many games as Valla and unlocking the master skin. This build is built around the play-style of simply using your auto attacks as much as possible with all of the life steal that you have and attack speed and damage to go along with it. With this build it's easy to stick around in fights and to prolong them in order to pull them out into your favor. Since you don't get Manticore in this build, it doesn't really matter what you attack in fights, as long as you are attacking something and lifestealing in order to keep the fight going (although proper targeting makes things much easier and quicker). With this build I feel you can play it into anything really, but the hero that you really need to look out for is because if she sneaks up on you and gets her burst off, it's hard to trade back at all due to her high burst damage.

Rancor gives you increased auto attack speed, so with your kit based around you using as many auto attacks as possible, Rancor makes the most sense.

More auto's = more lifesteal = more damage

Vampiric Assault gives you what you need to start harassing, and to keep you in lanes and on the map. Lifesteal keeps you in lane, in fights, and on the map which makes for the most logical pick up for this build.

Searing Attacks gives you the extra damage output you need since you aren't building Manticore or Giant Killer in this build. The extra damage can give you the ability to turn fights in your favor if your enemies don't respect your damage with this activated. Also with this extra damage boost, you get more lifesteal out of your auto attacks due to your higher damage which helps to keep you healthy in team fights.

Rain of Vengeance not only allows you to lock up and burst teams or singe champs, but it give you more time to re-position and get a few auto attacks off for a little extra hp that could help change the tides of the fight, or just to keep it in your favor.

Tempered Discipline works so well with this build because max passive stacks, you gain additional lifesteal which makes everything about this build as a whole way better. With this build, since you should just be constantly attacking whatever it is you can in team fights, if you get low this bonus lifesteal can be the life saver needed to make fights winnable.

This is hands down the greatest ability you can choose to level up because with this awesome safety gadget, you can change the outcomes of fights instantly and you gain hp upon activating. If at all possible it's best to try and use Blood for Blood on the person on the enemy team with the most hp as you receive 15% of the targets maximum hp.

Nexus Frenzy is simply the icing on top of the cake for this build as gaining 20% attack speed and attack range makes everything about this build better overall.