UPDATE 8TH OF JANUARY 2018: THIS THREAD WILL BE REMADE FROM SCRATCH ONCE THE SEASON STARTS.

Hey guys, since our Sub has grown in numbers beyond expectations, and we're continuously getting new moon worshippers, so the suggestion was made for me to put together an FAQ sticky with the communities help, here's the result:

What's a popular build on Diana?
I'd say the Arcsecond build is, RoA, Merc treads, Nashors, deathcap/void into zhonyas/GA.
Another popular build is an assassin type build, so like: Triple/Double dorans into Ludens, sorc shoes, Deathcap, void, abyssal and zhonyas.

What are good runes and masteries for Diana?
Mid lane: 9 Magic Penetration marks, 9 health per level/Flat armor seals, 9 MR/MR per level (can go 6 scaling cooldown reduction with 3 Mr/lvl) or just scaling AP glyphs, matchup dependant really. Then 3 AP quints.
Mid lane masteries
Jungle: 9 Attack speed marks, 9 health per level/flat armor seals, 9 MR or Flat/Scaling AP glyphs, with 1 armor quint and 2 AP quints (if you took health per level seals, if not just 3 AP quints)
Jungle masteries

Diana's viable positions
Mid, jungle and top (in that order in terms of viability).

How is Diana top? Can I get info on Diana top?
Diana top sucks, sorry to those who play it. Yes, it can work but for the most part the matchups aren't very fun (Darius, etc) and the lane is so long, meaning that camping her and denying her is really easy. You can easily make it work, but once you get to higher elo it's not very effective.

Hey guys I just figured out this insane 1000 degree 200 IQ 4D chess Diana build, it has [PICK 2]: Attack Speed, On Hit, Tank, CotC, AD, ADC. What do you guys think of it/has it been done before/is it good?
Yes, it's been done before, some are ok, some are fun, some are useful but for the most part they'll never be better than full AP due to Diana's AP ratios (until rework anyway).

How do you play Diana in lane/I suck in lane with Diana, how better do?
Very generic, but get vision and play like a bitch and don't push until 6 and farm under tower, once you're 6 you can make calculated engages if you know their jungler isn't close to mid.

What are Diana's hard matchups?
This is different, some players might not struggle with some matchups, but some of the harder matchups are: Morde, Cho and Swain, then there's the likes of Cassiopia, Leblanc and Ahri etc that you'll lose if they're good on their champion.

How do I generally play Diana? (Consistent Answer: Play like a bitch til 6, shred face post 6.)
Splitpush and flank, play around vision and don't really engage teamfights, try to flank. :)

Is Gunblade good?
It would be if we had 8 item slots, other items are just better.

Why is Diana offmeta/has low winrates?
She's too all in, with no escapes or anything. She doesn't exactly have LOW winrates but it's mostly because she's easy to deal with in higher elo and very camp-able by the enemy jungler.

Diana jungle build?
Skirmishers sabre runic echoes, sorc shoes/merc treads, nashors, deathcap, voidstaff and zhonyas/GA.

What Diana playstyles are there to pick from?
Psuedo ap-tank-bruiser, offtank (RoA, abyssal, zhonyas & GA in the same build), splitpusher, assassin and so on.

Lich bane vs nashors?
A common thing we get, but they have different purposes, Lich is more of an assassin item whereas nashors is teamfighting/splitpushing - Arcsecond quote on Lich bane: "It would be a good 7th item".

R Q combo, possible and worth it?
Possible, yes, however probably not worth the effort it'd take to learn and if you learn it, it'll be very unreliable.

Any recommendations on summoner spells?
Flash TP for mid, TP is just all around better for Diana, gives you a free lane phase, saves your lane if you get camped and lets you splitpush/make tp plays. Ignite is for strong laners pre 6 to give kill pressure, Diana simply doesn't need it - Exhaust can be used in some matchups but generally would go TP.

Any tips for Cassiopeia and Ahri?
Don't let them poke you pre 6, use your R reposition to dodge Ahri E/Cassio R, can also bait ahri's ult/cassio w, before fighting.
Work in progress, please post questions here that I can add to the list.