Ninja Tabi - The attack speed is really gonna come in handy until you can buy Qins or Executioner later on. The extra mana really helps in the early game.

Serrated Edge - Since Arachne has no dash/leap, you're really going to want to make the most out of your Movement Speed. This sword is one of the few items left that gives you +10% Movement Speed plus the other stats are really great, some Lifesteal to help you sustain along with your Venomous Bite. Since you want to all-in on people by using all your 3 abilities at once, the passive is really easy to proc, and it'll help you take down your targets quicker. Even after the upcoming update to the item, where the extra Physical Power and Lifesteal depends on how many of your skills are on cooldown, you'll be able to sustain on minions more easily without having to use your Cocoon on them.

Stone Cutting Sword - With this idea in mind to have as much Movement Speed as you need, this is what you want to buy. A really good amount of Physical Power, +7% Movement Speed (down from +10% a few patches ago), and the passive is gonna help you shred through Physical Protections as well as giving you some extra Physical Protections to box with your direct opponents.

Shield of Regrowth - Now comes a defensive option, which I really like to go to since I don't really like 100% glasscannon builds. This shield is not so expensive and will give you some great HP5 and MP5, a little bit of Cooldown Reduction (which you don't need at all on Arachne since you want to kill one guy with one use of your complete kit, and then on to the next guy), and +300 Health that'll help you against both Physical and Magical Damage. Now I love the passive on the item : +40% Movement Speed is a HUGE boost on Arachne. You can use it in various scenarios : the most common, use your Venomous Bite on someone, take a few steps away, watch them panic, use some stuff on top of them where they assume you'd be but you aren't, then walk back in once the way is clear and you feel like you can kill your target as fast as possible ; when being chased, you can just hit an enemy minion, a jungle camp or the Wild Juggernaut to gain some extra Movement Speed to run away.

The Executioner - Now since Arachne's a basic attack character, you're definitely gonna need Attack Speed. This weird-looking axe is gonna give you +25%, as well as Physical Protection reductions (it has been nerfed in the past but is still good) and some Physical Power. At this point, once you've stunned someone with your Cocoon, he's gonna have 3 stacks of The Executioner and Stone Cutting Sword and he's gonna be a free kill, even if he's got some Physical Protections in his build.

Qin's Sais - When you feel like you need more Attack Speed, go for this. It used to give +15% but now it really challenges The Executioner with its +20%. Buy this if you struggle to take down enemy tanks (and have to, of course you're not gonna focus them in the first place), or if the enemy mages have Warlock's Staff, Soul Gem or any other Health item. Against gods with 2000 Health and less, Qin's Sais is gonna deal 60 extra damage per auto-attack, and it'll go up to 137 extra damage to gods with 2750 Health and above.

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Don't forget to replace your boots once you get the elixir of speed.

Bloodforge - For when you feel really comfortable in the game, as a 6th item, when the game lasts for half an hour and more, this'll help you go on killing sprees with the extra Movement Speed and the Health shield it provides on takedown (lasts for up to 20 seconds).

Asi - If you lack some Attack Speed for some reason, this item has lots of things you need : Attack Speed, Penetration, some Lifesteal that can help you survive and take down an opponent before they kill you, when you drop below 35% Health.

Winged Blade - Feels a bit redundant with Arachne's slow immunity on her Web but overall a really strong item, even with the bonus Movement Speed going down to +7% from +10%, when you have a hard time dealing with a Nemesis or a mage with a Gem of Isolation. 1850 Gold for 300 Health and the passive is a really good choice : slow immunity and +20% Movement Speed, you're basically untouchable.

Toxic Blade - You can't really proc brawlers efficiently on Arachne, and the stats on this blade are all useful for her. A strong anti heal item (even with only 2 max stacks down from 3 in the past) without compromising your damage output so much. And some Movement Speed.

Magi's Cloak - When sometimes an enemy's CC is giving you a hard time, just buy this and walk right through it. It's available every 1 min 10, along with your 2 min 10 beads, you're gonna be fine. Another item with 300 Health for only 2150 Gold.

Mantle of Discord - Hands down the best defensive item in the game in my opinion, if you had to buy one single defensive item each game, buy this one, no matter the god you're playing or what there is against you. Some really good protections on it that makes up for the lack of Health, and an extra +10% Cooldown reduction. The passive can either give you time to press your ulti and walk away, give you enough time to turn on the guy trying to assasinate you (especially Loki, be careful though if he procs it with his ult, he's gonna be CC immune and you're gonna die anyway), or give you an extra second in a 1v1 fight to have the edge on your opponent.

Frostbound Hammer - It's not really necessary considering you don't have trouble to lock people down with her kit and your build, but if you're having a hard time against someone (a King Arthur for instance, a Tyr, or some other Warrior), you can buy that. It's another 300 Health. It can be really strong in the late game to box the enemy Hunter, because it slows down their Attack Speed. And it helps your team follow up more easily on the guy your hunting down : in general, you're really fast and chasing enemies down but that means they can still run to their towers and/or allies to get some help, with Frostbound Hammer they won't have this option, and your teammates are more likely to give you some help.