Until you have your Hexcore upgrade for your E, you don't push backline minions in one ability cast, therefore, you don't want to get yourself in a situation where you have a very few seconds to clear the wave and not quite make it, so intead try to freeze the lane whenever you can, using your Q shield to not get any damage from minions, deny enemy cs, and/or go for recall. You should only start pushing when you know you are safe doing so, or when you have cover from your jungler/team...

Since lost chapter is cheaper, you won't ever need tear for mana, and LC is a huge legendary item spike for Viktor which pretty much unlocks his ability to trade effeciently, and win even hard matchups through poke.

During lane phase you are trying to poke your opponent with E, as long as there is some objective to be reached, such as making the opponent recall before getting a certain item power spike, getting them on low hp so that they have to be afraid of jungler, poking them before taking major objective (tower/dragon/void krugs...) etc.
However, your E mana cost is pretty high, so unless you have blue buff, you have to be very careful with how you use your mana.

Viktor is hyper-scaling carry, which means he is an insanely powerful late-game pick. Therefore, if you just get out of the lane phase even, you are always winning.
Enemy objective should be to either shut you down in early game or outroam you and win other lanes, until you to about level 11 / 2 items power spike.

If you play Viktor against smh like Qiyana, she might win the game until you get to your first item power spike, thats just something that happens in soloq once in a while, but you can try to avoid that by always pinging your opponent missing etc. And freezing cs away from her while she roams

With each Glorious Evolution(Viktor's passive) upgrade you get one basic ability improvement. At 3 upgrades, you have upgraded all 3 of your abilities and therefore your ultimates gets it's upgrade as well, that's an important one as you pretty much have Rylai slows on your spells.

Perfect item for Viktor, super-boosts ultimate, you also get 20 Ultimate Ability Haste, which makes you able to also wave-clear waves whilst, mostly, still having your ult for fights.

This new version of luden, the companion, is just the old classic, makes you push wave a big faster and gives you annoying poke with your laser.

This item is a must have if more than 2 enemy champions are building magic resist. You should build this item later on in the game no matter what since durability patch(as 3rd or 4th at latest) even if enemy players do not buy a lot of magic resist. The later on in the game it is, the higher value this item has.

Great choice against melees, also gives you MS which can make dodging skillshots and overall movement better. This item a style preference, as it alternates Viktor's playstyle a bit, but if you find success with it feel free to build it pretty much every game, just don't skip void staff over it if enemy is building MR and you should be good to go.

Similar to lich bane, as it also gives MS and you want to build it at similar points of game, amplifies your bursts and can earn tiny bit of gold.

Since Viktor is immobile, the MS which cosmic gives can come in handy. Nice item if you don't have to build anything else.

Strong against tanky team comps, if enemy have 2+ tanks, buy it. You can buy this item later on in the game even if the enemy enemy has just one tank, it's value even against squishy champions is decent because all champs scale with HP greatly, especially after durability patch.

This item amplifies your damage like crazy, if you are solo ap and enemy won't build MR

Viktor is a heavily scaling mage, which means he wants to farm for about 3 items and then your heavy power spike comes into the play. Champions with such win conditions usually profit from Rabandon nicely. MUST-BUY every game 4th item or earlier.

On 14.3 Seraph price was lowered by 100G, at times like this when the time value is just worth-it you can go it any game because Seraph will be always a good scaling option, and early tear for Laser spam will always decent way to win any lane.. Anyway, general theory about this item: You can go tear if you are playing against a tank in the lane, like singed sett ornn etc. I'm not sure about tank mmrs, but in highelo you can experience pretty much anything, from malphite ornn sion to mundo in mid once in a while. In such scenarios, when the opposite laner is just eating your poke and hoping to run out of mana you can go tear for laning phase to slowly shoot him down. Howerver, don't put high priority on finishing the archangel's staff sooner than as 3rd item. Also keep in mind that this item is not very strong before it evolves into Seraph's Embrace, so don't finish it unless you have tier fully or nearly stacked.

Viktor has no escape as well as relatively slow cooldowns later on in the game. Therefore using your whole combo, zhonya into another spell rotation is very likely scenario in fights. But most important reason behind buying this item is Viktor's lack of escape. Since S14, this also gives a lot of AP, so you don't lose much either.

This is a very niche item. Good for games with a lot of jungle fighting where the extra vision is helpful, keep in mind this doesn't reveal Akali/Twitch etc. :(

Great item against champions such as Ahri, Syndra or LeBlanc. Since S14 you don't lose any damage since it gives a ton of AP and the MR numbers it gives you are insane, especially against champions that profit from flat magic pen, and makes you nearly an unkillable threat against stuff like Ahri that demand on bursting you in one combo. If you buy this item, you usually don't have to go Mercury boots and therefore you can opt-out for the ideal boots options - Sorcerer's Shoes.

Crazy cheap.. If your teammates don't want to build healing reduction and enemy has a lot of champions with healing in their kit (such as Dr. Mundo, Kayn, Olaf etc.) or many lifesteal items, you can build this. Once you reach full items, if you team built heal reduct by then, replace it.

Okay, hear me out. This item gives you HP, is cheap, gives you medicore AP and Haste, BUT, makes you have a dash on Viktor. I THINK this could be very situationally, almost a broken item choice. Helps you with escape and chasing down enemies. Sometimes a dash can be much more valuable than zhonya or banshee, if you just escaped hook, arrow or some other key, game-changing skiillshot.

Useless since Viktor's abilities rework, and the slow you get in your kit (W upgrade).

Boots

Default choice, useful especially if enemy don't build a lot of MR. Howerver, you can't always afford building these instead of safety boots. If you see early on that enemy team is already buliding a lot of MR, get some other boots instead and build Void Staff.

Good buy if you have 950 base, will always bring it's value. Especially good if enemy build MR (No Sorcerers angle) and you don't need Mercs either.

Safety choice you might end up going for most of the time. Must have if the enemy team has a lot of CC and you are not running cleanse. Great item especially against champions like Ahri LeBlanc or Syndra. If you don't need the tenacity, but just the MR part, you can just buy one null magic mantle into your inventory, build Sorcerer's Shoes instead and then finish Banshee's Veil later on. Finished Mercury Treads give the same amount of MR as just the flat null magic mantle.

Solid boots choice especially with team that you need to kite and/or have ton of slows but not much hard CC.

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