Vladimir is one of the most viable AP carries in this game. Although people keeps on nerfing him, he is still a good choice. The god like mid game carry (level 9~16). He is extremely easy to play, the ability of using Sanguine Pool is the only factor that can determine whether you are a good vlad or not.

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Before 6, just play passive and keep your health above 80 percent. Around 7~9 start being more aggressive and at level 9 you are the TRUE Vlad. Q harass until you think you can kill/dive your enemy. Flash, ult, Q, e, w, Q. During levels 9~16 try to establish a huge advantage for your team, so that you guys can win the game before hitting late game (in other words, when Vlad start to become more and more useless). Late game positioning is very important, Q back up, e, q back up, e. That's the main sequence. You don't necessarily have to initiate every team fight with your ult, cuz if 1 stun or silence gets you, you are pretty much dead (no health vlad = useless). KEY: ALWAYS SAVE SANGUINE POOL! Unless you are chasing, or else that's one of the most OP spell in this game.

Why Magic Pen red? You know the answer.
Why Armor yellow? Reason: #1 cheap! #2: Vlad's most crucial weakness is during early game (1~7) and 13 armor will help reduce some dmg. But if you are rich in IP, then get health per level or health regen per level.
Why flat CDR blue? Well, just for sanguine pool and hemo plague to be on lower cool downs early in the game. Eventually you will solve the problem with Blue Buff, or Ionian boots+spirit visage. Or you can ignore the CD since late game fights won't last that long >.> and all spells have reduced cool downs.
Quints: 3 health quints is another option. I Magic Pen quint is just to make the number look better >.> from 8.5 to 10. Flat health's purpose is to make you more beefy early game and more durable in lane. Don't need to get 3 magic pen quints because they are useless, and 10+Sorc shoes+Haunting Guise give 50 Magic Pen. Already doing true damage to heroes that don't have. MR.

Max Q (for all kinds of play styles for Vlad)
I personally prefer pool over sides of blood, not to do damage, but for lower cool downs on suck a useful spell.

Starting items: Price was increased on Doran's shield so that you can't get a health potion. As a result, it's not a good option to just get the shield, since healing/regenerating health is very OP early game. So 3 health pots is very good for keeping you in the lane. Boots as first item over amplifying tome because of the mobility advantage that you get is more important then the damage. Why? is helps you get to places faster, escape ganks with the combination of your pool, and chasing people.

First trip back: Ideally get Sorc shoes+Giant's Belt. If you are short on gold then buy Sorc shoes over anything else. Why? Mobility advantage and Early Magic pen is very important and strong on Vladimir. Get some health pots and wards if needed.

Mid game items: Sorc shoes + Rylais. THAT IT! That's all you need to carry the entire mid game. YOU ARE SOOOOOO STRONG. Ideally your enemies haven't gotten any big MR items such as Banshee's, Force of Nature ... etc. In that case you should buy a Haunting Guise, which mean you are pretty much doing true damage to you enemies because usually Champion's MR stay at 30 (unless they are tanks or melee, but your targets are squishy carries that has their MR stay at 30).

Late game: Always get a Death Cap to Amplify your damage. Depending on the situation, you have many choices.
1. Go tank, get Sunfires and Force of Nature. Sell Sorc shoes for Merc Tread, sell Haunting Guise for get a Randuin's or Banshee's or Abyssal's or GA depending on the situation.
2. Go CDR, sell Sorc shoes for Ionian boots and sell Guise for spirit visage. Buy Void staff, then Zhonya's or Abyssal or GA depending on the situation.
3. Continue with your AP build, get zhonya's and void staff or Abyssal.
4. Go Troll, Ad vlad, wards vlad, Elixirs vlad, ... etc. Use your imaginations >.>

Always try to out farm your enemies, even when you are loosing. Farming with Vlad is also extremely easy..... E,W..... or E QQQQQQQQQ..... or ult (doubt anyone will use this, but it's still an option XD).