So I'm sure many of you might be bored talking about Mr. Tentacles, but I feel like a number of people have gotten the wrong impression. This is mostly due, I feel, to the champion spotlight that completely missed the mark with representing his strengths and weakness. I'm going to tell you what I found about the cephelapodic sage playing through a few games as him.
TL;DR Laning phase is fairly lackluster, focus on penetrationhuehue, and learn to be patient and time your skills right.
I want you to keep that last part in the back of your head, that one's a biggie. ______________________________________________________________________________________
So i went into my first normal game as him, excited to get to feel how Vel'Koz would pan out in PvP. I had already tried him in bots, so I already had a feel for how his skills work and how I wanted to build him. It was fairly close after his release, so the poor Syndra didn't properly get how to dodge My Q, and was likely quite flustered. I managed to push her out of the lane very frequently, farmed up, and came back to lane with my chalice. Time to spam all the abilities!
I became a bit of a problem alongside our top lane Yi, and the enemy surrendered at about 26 minutes, no longer willing to deal with the insane damage my Deathcap'd laser was pumping out. I felt good about the game, but needed a bigger sample pool before making any determinations.
My next game pitted me against a Yasuo. Although much more mindfull of how my skills worked, I still managed to bully him around fairly easily. Fun fact: Only my Q is blocked by the windwall. I won my lane fairly strongly, but something happened in the midgame. I had my athenes, I had a needlessy large rod and was working towards my seekers. But still, I didn't feel like I had much damage. Only when my passive got proc'ed would I take significant chunks out of my enemies hp. And man, did Yasuo make my combo difficult. We still won, but they almost came back. Overall, I didn't feel like I gave me or my team any real advantage with my success in lane.
My third game was a few days later against a Leblanc. I don't think I need to elaborate how handily she spanked my ass. Dat silence, man.
My following games had a similar pattern to the last two, I simply had a hard time landing my comboes in lane and , even when ahead, wasn't having an impact later.
So I was browsing Vel'Kozby's wiki page, maybe looking for some insight as to why Vel'Koz seemed to be miserable in the midgame without a head-and-tentacles lead. That's when I stumbled across Marat569's comment. He talked pretty in-depth about how he approached Vel, but the one thing that immmediately stood out to me was his recommendation to rush a Haunting Guise. It struck me how simplistically brilliant that idea was. I couldn't beleive it didn't come to me sooner. Of course Vel'Koz would benefit greatly from not only the HP, but also the spell penetration (I'll detail that later).
Several games and one very upset Lux later, I confirmed that this clearly was the superior option to a chalice, and also opened me up to a better way to play Vel'koz than just a spell-spamming, wave-clear machine.
Now to elaborate the way you should look at Vel'Koz, at least as a meta mid-laner. ______________________________________________________________________________________
First of all get it out of your head that he is a long-range harasser. Cut it out. He is not Ziggs. I repeat, he is not Ziggs. He is not Lux. He is not Xerath. While his skills have fairly large range, and you can snipe people with well angled Q's, this is incredibly unreliable and you will waste mana and precious cooldowns. As far as laning and 1v1-ing people goes, he is a mid range mage. The best way to think of this is with Morgana. Sure, her skills have pretty good range, but the closer you are to your enemy, the more reliable you can land your snares and set up your ult. Same thing with Vel'koz. Be maybe 100-200 units within the max range of your E. "But sir", you may mockingly rebut "that will put me in close proximity to mine opponent." Yes, yes it will. Get used to that, you will have to spec for it. Double-dorans is very good idea, or again rushing the The Mask for trading power.
Don't trade often though. Your early damage is fairly weak if you can't get your passive true damage off. Focus on farming, and only concede to fight when it matters. It is better to wait for your enemy to be out of position and land a surefire E-W-Q-W rotation than to fish for hits because you have the mana and cdr to do so. Junglers, if you anticipate your allied piscodemon will be forced to fight a lot, maybe show them some love with a gank or a blue-buff.
When you do go in to trade or duel, focus on landing your W. That is your main damage ouput. Everything else is just to make it easier to land your W. The ratios on the two hits are not that strong, but the total base damage is pretty solid. Additionaly, it is two seperate hits that proc spell effects each time, not just your passive. That is the key thing. That means that with 30 spell pen from boots and Majora's Mask, you will ignore a total of 60 MR: 30 on the first hit, 30 on the second. This is why penetration is so strong on him. As a rule, if you're not sure you can get three spell hits to get your true damage, it is not worth the trade. Without the passive or some spell pen, your early damage is garbage.
You need to shift your frame of mind in the mid game for team fights. You will not be dueling people in mid-range combat. In fact, you won't be doing anything other than pressing the R key. I'm not joking. Tentacruel's team-wide impact comes from his 500/700/900 base damage plus true damage from the passive. And you can't just press it haphazardly. This is where the patience and timing comes in. As Vel'koz, it is perfectly acceptable to wait 3 whole seconds after your Wu-Kong ults into the enemy team to follow up. As I said, your primary goal is to line up for the most beautiful, un-interrupted, whoop-shooting laser that you can. Your other spells only matter so far as to keep your enemies in position for your ult. Ideally, you will have someone like Amumu or Jarvan who can do all of that for you, so you don't even need to think about your other abilities. This is why Vel's ult has such a big range. It's not because he plays at long range, but it's so he doesn't have to be so close to the front line in order to hit the enemy back line. So remember, proper ulting is the only thing that matters in the mid/late game. Always be envisioning the perfect ult. Breath the ult. Become the ult. ______________________________________________________________________________________
Now for items.
Forget Athene's. It tears me up to say it, as I have a massive league-boner for this booze-cup filled with magical happiness, but you do not need it. Remember when I said all you will be doing is pressing the R key? If you focus on that, you won't ever have low mana except maybe immediately after cleaning up a fight. You don't need the cdr, the base cooldown is 100-70 based on rank. If you expect to fight a lot during lane, maybe pick up the double dorans. Get blue buff if you can. Athene's is a crutch and getting it will just trick you into wastefully using skills when you don't need to. You can siege with Vel, but its not what he is good at. It's difficult to be in the proper position to ult someone under their own tower. Don't go fishing for knock ups or skill shots. The cd on your W and E are fairly long and very precious. Save them for when they matter, when you are assured to hit them, or when Bruce Lee Sin is hidden-dragon-ing towards your four-eyed face. Don't let him do that.
As I mentioned before, penetration just makes sense for Vel'Koz. Haunting Guise is a strong pick. There is the double proc on his w, and of course his haymaking ulti. The ratio on the laser is only 0.6 on a full channel, but the base damage is huge. In general, it is better to go with high penetration than raw AP on champions with large base damages. I'm not sure if the pen procs on each of the five hits, or is calculated as one hit then spread over the five, but it's still 900 base damage. Plus once you get a Liandry's later, the HP burn will be empowered by the slow effect.
If for some reason you are completely curb-stomping your lane and you can afford it, maybe grab an abyssal sceptre. In lane you'll be close enough to get the aura effect. It's not as great late game, when you should be farther back from your targets, but it will shut down your lane opponent hard if they are AP.
I might hold out on a void staff, though. If it goes to late game and everyone is packing a good amount of MR, then get it.
Rylai's is another strong pick for Vel'Koz. The HP is a nice buffer, and the slow is a very good accessory for the fabulous flagellate. It's true that it gets reduced to 15% since most of his abilities are AoE, and will only stack up to 5% on his ult. Though the numbers say it won't be impactful, I say that in game you can feel it working. And again, a high AP item is not as effective on him with his weak ratios. If you really feel like you can do without the slow, a RoA gives the same AP and beef with some bonus mana.
Again, I don't think that when you properly ration his spells he doesn't needs a lot of regen or a large mana pool, so I discourage getting a tear. Seraph's shield is nice to have and the item does synergize very nicely with the purple pimpcane, but again stacking AP isn't that strong.
And just as I say that, I will recommend a Zhonya's. I would say it is a toss up between this or a Deathcap (you do need to have some ap). If you expect a lot of diving to happen, like with a Zed, an Hourglass is really helpful to dodge and delay damage. ______________________________________________________________________________________
So there it is. Vel'Koz is not the spell spaming artillery cannon Riot tricked you into thinking he was. Go play AP Kogmaw if that's what you want to do. Don't complicate you approach with needless mana. Focus on your ultimate goal: melting the entire enemy team in a C'thulu Staring Contest. Practice positioning. Practice patience. Build Liandry's. Star in a hentai production WHO SAID THAT!?
EDIT MARCH 11: There is a trend in the replies, so I'm going to point out a few things to pre-empt future views.
As a few have already pointed out, there was a slight derp with explaining the MR in relation to the W. I math'd it, and it the difference is like 0.0001% of the damage between 1 hit or two. It still has a strong base value, so penetration is still helpful.
The item set I put out above is just illustrating the major point that cdr and mana shouldn't be the focus when building, and gave some alternatives I have used. It should go without saying that any build strategy should be flexible and reflect your enemies' strategy with their abilities and items.
As a post-script summary, the idea should not be improving the frequency with which you use your skills, but maximizing their impact and effectiveness when you do use them. Vel'Koz is too vulnerable to waste even 5 second cooldowns; you need to land your E to hit your W, and if you miss your E, then you are a sitting duck with no defence. I have seen a Katarina literally do nothing but shadow a Vel'Koz, wait for him to use his E, and immediately jump on him because she knows he can do nothing but lie on the ground and roll over.
In short. quality over quantity.