Diana: Thoughts and Discussion
Ever since Diana was created she always felt SLIGHTLY Akali clone-ish, which kind of means the better of the two is the one that gets played more / competitively.
In terms of better counter play and better define Diana for her own unique attributes stand out better:
~ Greatly reduce Diana's burst damage and better emphasize her as an ability power scrapper and diver, someone who builds squishy, but has ways to stay alive by utilizing her sustain damage and shield.
~ Make her unique vacuum ability (Moonfall) an even MORE powerful moment of power with a greater vacuum effect vacuuming enemies all the way to Diana's location, via make Moonfall Diana's ultimate.
~ Move Lunar Rush to her E slot to remove its damage and grant the slow to that, this allies for that sticky diver gameplay and removes Diana has a quick 100-0 burst champion emphasizing Diana with sustain damage even better.
~ Create a kit around Moonsilver Blade (passive), which emphasizes that scrappy nature and grant more rewards with the proc, i.e. lower Diana's shield duration by a lot, but Moonsilver Blade procs resets the cooldown (so as long as you are fighting you can potentially get a permanent shield); Nashor's Tooth will be of an even higher priority with a change like this.
~ Remove Diana's bonus attack speed passive and just give her a higher base attack speed, also rewards Diana building Nashor's Tooth further (I think it is cooler to see an AP melee champion going for Nashor's Tooth rather than Lich Bane)
~ Q moon marks allowing for Lunar Rush resets is cool. Just wanted to say this. More detail, allowing the option for the short cooldown Lunar Rush for landing your skill shot or just for quick double Lunar Rush on a high cooldown has a lot of cool strategies to it that of course needs to be preserved.
~ Swapping Lunar Rush and Moonfall around with the E and R slots also helps out jungle Diana this way, besides giving her a true moment of power ultimate on a long cooldown to look forward to at level 6 rather than just becoming useful at 6 and useless pre-6.
THE ONLY REASON I DO NUMBERS IS FOR A BETTER EXAMPLE, THEY DO NOT MEAN ANYTHING FOR THE GRAND SCHEME OF THINGS. APART FROM, FOR EXAMPLE, HIGH AP RATIOS FOR LOW BASE VALUES TO DISCOURAGE TANK BUILDS.
Base Attack Speed: 0.694 +2.25% from 0.625 +2.25%
PASSIVE FEEDBACK: [3 attack bonus magic damage from 20 - 250 (+80%AP) to 25 - 250 (+100%AP), but divided up into 3 attacks instead of one super strong cleave attack to move it into even more of a sustain damage ability rather than feel bursty (more emphasis on the cleave still)]
Moonsilver Blade (Passive): Diana deals 5 - 50 (+20%AP) bonus magic damage on-hit. Every 3rd basic attack within 3.5 seconds increases this damage to 15 - 150 (+60%AP) bonus magic damage as a cleave.
Crescent Strike (Q): 10/8.75/7.5/6.25/5 seconds; Cost: 50 mana; Range: 900 units Diana unleashes a bolt of lunar energy to the target location in an arc, dealing 60/90/120/150/180(+70%AP) magic damage and afflicting struck enemies with Moonlight for 3 seconds, revealing them for the duration.
Pale Cascade (W): Cooldown: 10 seconds; Cost: 40/45/50/55/60 mana; Range: 200 units Passive: Damaging enemies with Moonsilver Blade's cleave attack will refund Pale Cascade's cooldown.
Active: Diana shields herself for 30/40/50/60/70(+40%AP) for 1.5 seconds and creates three sphere that orbit her for the duration, detonating upon contact with an enemy and dealing 15/20/25/30/35(+10%AP) to nearby enemies. If all three orbs detonate then the shield duration is refreshed and 30/40/50/60/70(+40%AP) additional shield is added on.
Lunar Rush (E): Cooldown: 26/23/20/17/14 seconds; Cost: 50 mana; Range: 800 units Diana dashes to the target enemy while slowing it down by 20/30/40/50/60% for 1.5 seconds.
If Diana dashes to a target inflicted by Moonlight then all Moonlight is consumed and Lunar Rush's cooldown is refunded.
Moonfall (R): Cooldown: 120/90/60 seconds; Cost: 100 mana; Range: 600 units Diana draws in all nearby enemies all the way to her location and dealing 150/200/250(+100%AP) magic damage while slowing them down by 99% for 1 second.
UPDATE: Lowered Lunar Rush's slow to 20-60% from 20-80%; reason why +5% scaling is not good is because it makes it a forced max last since it is not good enough to sync further points in. When the rank up feels pretty good to the player then ability max order comes down to personal player expression rather than what is clearly the worst and best.
Also Lunar Rush would still apply the auto after the dash here, so its "damage" would be what Moonsilver Blade's damage would be (plus 100%AD because basic attack), whether the weaker on-hit or the cleave damage.

A scrappy AP fighter that already exists and isn't a clone of Ekko.