SoIMBA.Com's Wisp Guide, This Ball is Making Me Testy

My rationale for Shivas is that it provides additional tankiness while also providing anti-carry potential and an extremely underrated active ability (the damage is meh, the effect is great, the vision it provides is icing on the cake). The reason I'd go for it as opposed to AC is because the attack speed it provides Wisp is a complete and total afterthought, in addition because of how attack speed (DR) scales with Overcharge it's essentially a waste. Comparing the two items:

AC gives an aura that provides allies with 5 armor and 20 attack speed while reducing the enemy armor by 5. Shivas does not provide an aura but offers you 30 int (not a big issue at this stage of the game, but still decent to have) but does give a 30% attack speed slow while people are in range of the aura. -30% AS is a MASSIVE consta-debuff if you're able to position yourself correctly and I think is more important come late game. The other reason that I include Shiva as opposed to AC is that your ideal partner for Wisp is a strength carry and most of the viable and popular strength carries are going to make an AC for themselves, thus making it unnecessary for Wisp to buy one him/her/itself.

The reason behind Eul's is that I have an unnatural love for it. While Blink Dagger helps yourself (which is fine) it doesn't necessarily help a teammate. The entire idea of support is to allow your carries and other teammates do the lifting while you take care of the dirty work. Eul's allows you to take pressure off of an ally who's either being focused down by multiple targets or needs to get away. The other reasoning behind my love of Eul's is that I've found that it helps a lot with Relocate ganking because you can cyclone yourself to buy time for the 12 seconds to be up or if you're ganking and an enemy comes to help their ally.

tl;dr
Your carry will usually get an AC, that's why I like Shivas although I don't think AC is a "bad" pickup if your carry isn't getting it. Eul's I just love.

I registered just to post here and vote for this guide. I am myself a wisp player on vhigh with ~68% winrate over around 200 games, and I agree with everything you have written, especially your skillbuild. Overcharge at level 4 is very important when you are babysitting a carry, I find it sad that some competitive supports overlook this fact just for a 0,5 second stun. The times i've used overcharge at lvl 4 to save my carry through regen are countless and no 0,5 second stun would ever compare in such a situation. The only reason to ever ignore overcharge at lvl 4 would be if you are solo mid or you play with a carry that doesn't need any help in the laning stage. Even then I would consider getting 1 point in overcharge around lvl 7-8 when the midgame kicks in.

I agree with pretty much every itemchoice except for the intelligence items (shivas, guinsoo, euls), what is your thought there, is it personal preference?

Shivas is 4700 gold for 15 armor and some damage + aura, I understand what the item does, but I question if there isn't anything else to get for the same price with a higher impact, such as assault cuirass.
Guinsoo is perhaps the most understandable item, since it is amazing on any hero.

Eul's however, I dont understand. It's essentially a disable giving you 0 stats for 2800 gold, wouldn't blink dagger be a better choice for both escaping and blink+tethering someone? Please do give me the thought behind euls.

I did originally put the first point of Overcharge at 8 but I tend to get a level of OC early in order to stimulate tether regen. To be honest it's about a 50-50 split for me, depending on how the lane I'm in is going. That being said, I never feel that the extra .5 seconds of stun makes that big of a difference, especially since it deals no additional damage. As for Vlad's I think it is a decent situational item, but I rarely find myself going it, mainly because our offlaner will usually go it if it will offer a discernible difference to our team comp (usually a situation where two of our 1-3's are melee and none of them are going lifesteal as an early option).

Very well explained guide, I haven't had enough time to read it all but it looks awesome so far!
Just a quick tip to improve your guide: competitive players usually put a second level in Tether at level 4, because 0.5 more seconds of stun can make the difference for an early kill. I also don't like levelling Overcharge if not at level 10 but, as I'm not that good with Io, I think it's a better choice to put one point at 4 (or 8) as you do.

Other than that, it's a perfect guide: you might want to add Vladmir's Offering as a situational item, as it helps your melee friends a lot and gives you more health regen that gets Tethered to the linked Hero.