Salutations,

I am The Vi Guy, and you must be wondering what drugs I'm on to get the idea to play Trinity Diana toplane. The answer is a lot of drugs, but that's beside the point.

Now, a lot of people would label this as an "AD" build and dismiss it, but truth be told, you do around a 60/40 split between magical and physical damage respectively, and you only build like 55 AD in total (if you skip the Mallet and go for something else for health, which i often do). It's a hybrid onhit build to be sure.

Personally I play it because I think this is what Diana should have always been - a bruiser.
She was never officially labeled as an assassin, being marked as fighter/mage currently, and she doesn't have an assassin pattern.
Her usual pattern is QR in, CC everyone, explode one target and then either die or murder everything else.
Assassins usually have "outs" after murdering someone, like Akali shroud, Zed second ult activation, Ekko ult, etc.
What Diana does is more similar to what, for example, Vi, Jarvan or Irelia do.
Her play pattern is that of a diving bruiser, not an assassin.

But all that aside, why would you play Trinity Diana as opposed to AP assassin Diana?
Pros:
• dishes out large amounts of mixed damage
• great initiation
• aura carrier - mainly Frozen Heart
• very hard to kill
• not only has high amounts of bulk, but is extremely mobile and can lifesteal too
• initiation potential skyrockets with Righteous Glory/Randuin's Omen
• very competent laner with a large power spike at lvl 6
• annihilates turrets (although this is somewhat true for AP Diana as well)
• You don't feel dirty for playing the balance mess that is Assassin Diana.

Cons:
• Has some very negative matchups (Pantheon and Nasus come to mind)
• No real lane pressure pre-6, especially vs ranged champions
• Not the easiest champion to farm with with this build
• Very reliant on her Q reset since RQW is no longer enough to murder someone, you need to stick to them as well for autos
• Build is expensive - may be forced to forego BotRK to go straight into tank if doing badly
• People will bitch about your build, even if you are 17/7/10
• Not as tanky as some other toplane choices, especially since you rush 2 items with barely any defenses between them.

Convinced? Interested at least? Then read on.

So how would you set this up?

Well, for Runes, this is my personal setup:It gives me everything I need really.

Alternatively, this was my old setup:
AS | HP/lvl | MR/lvl | Flat Armor
Good enough if you don't have all the runes I use.

You can do whatever you want here really as long as it makes some sense.

As for Masteries, This is my page:

Like with runes, you can really mix and match however you want here as long as it makes some sense.

For Summoner Spells, there's only one option really.
Teleport and Flash.
Flash is pretty much mandatory on everyone, and Teleport allows for unrivaled map pressure and helps you get back to lane.

Farm.

That's literally it, your job until you hit lvl 6 is to just survive and farm. That's why you get Crystalline Flask and pots. To survive and be able to spam Q to get far out farm more.
You can't really do much before level 6 and you generally should not be trying to fight.
You're generally weak vs strong lane bullies like Darius, Pantheon, etc.
That said, if they screw up, you can punish them.

For example, Riven can usually slap you silly in trades, especially pre-6.
But if she gets ahead of her self and goes for a trade before she is level 3 and has all her skills, even worse if she has Teleport instead of Ignite you can just stand there and bash her face in, and at that point you have a free ticket to lvl 6 and your power-spike.

So basically, you should be farming, but don't be afraid to trade blows when engaged on, unless they can dunk you.
Once you're farmed 1.2-1.3k gold, you should be around or just at level 6. At this point you should shove the lane as hard as you can and recall.
Immediately buy Sheen and some pots and just Teleport back to lane - or walk, if you think you won't lose CS to your turret because your opponent isn't counter-pushing hard.

Once you have Sheen and your ultimate, your trading potential skyrockets.
It WILL catch your laning opponent off-guard.
Just auto a minion twice to ready your passive, Q towards him, and if it hits, R>W and autoattack. That should take around a third to a half of his hp and he will generally back off a bit. Just walk away for now.

Repeat this "hit-minion > hit-minion > Q towards him > engage trade if hit" pattern as long as you have mana to sustain it, since it will zone him and allow you more opportunities to push up.

As you push, look for Teleport opportunities if some skirmishes erupt in botlane or around dragon. At lvl 6 and above, you just become a menace in skirmishes and can just indiscriminately dash around and murder people.

Speaking of:

At this point you should have your Trinity Force and Boots at least.

At this point you should have 400 movement speed which allows you to roam quite well, which you should be doing as often as possible, using Teleport more for assisting your team rather than just getting back to lane.
Diana is really good at counterganks with her easy mobility and Moonfall. If your botlane is in the process of getting dunked by 3-4 people, don't hesitate to Teleport in and add some chaos into the mix.

Your laning opponent may push and take your turret but I'd take crushing their botlane and securing dragon over my toplane tier 1 turret any day. This is the point where you feed your teammates kills (or leech off of their success if you did worse than them).

Work on pushing mid and taking dragon. Your role is that of a diving/initiating bruiser in the same sense as a Jax, Jarvan IV, Xin Zhao or Irelia.

As for items, you should be working on your Blade of the Ruined King at this point. If you need to be tanky, fast, you should look into buying a Recurve Bow and just sitting on it while tanking up, and either delaying BotRK or replacing it with Wit's End later on.

You should also finish up your Mercury's Treads somewhere in there as well which will give you a total of 420 (ayy) movement speed for even better mobility.

If you need to be the frontline ASAP, you should get a Randuin's Omen, but if you have another frontliner on the team, getting a Frozen Heart instead is much better. It may not have the HP, but the CDR and mana are lifesavers and it doesn't clog your build.

You generally should get Frozen Heart either way, so Randuin's Omen takes the place of your HP item, so you're not open to getting Frozen Mallet or Turbo Chemtank if you get it.
That said, Randuin's Omen is not a bad item by any means, and if you're vs a full AD comp or their AP isn't a concern, you can just skip your MR item for another HP or armor item anyway.

Once you've got your 4th item, you will slowly be moving towards:

Skirmishes will happen in the lategame, don't get me wrong, but more often than not, full-blown teamfights will be more common.

You have two choices here - engage or counter-engage. Diana is good at both, but she can't really disengage. If she's in, she's in until either she's dead or everyone else is.

For engaging, if you went the Turbo Chemtank, pop it, run at the enemy team like a maniac, QR someone in their mid-line, and E and pop the second active at the same time to slow them all to a crawl. Your team should be close behind to mop up. Focus their MVP and don't bother with their frontline. If they bugger off or die, you can turn to their tanks because your Blade of the Ruined King will still shred them.

Alternatively, during sieges, if you manage to clip a squishy with your Q, don't hesitate too much on just ulting them and blowing them up then and there, since you still pack quite the nasty burst even though you built for sustained damage. You probably won't instagib them like AP Diana would, but you will be able to survive until you have a second combo ready to unleash. That's why CDR is quite important, as is the Blade of the Ruined King active for chasing purposes.

Items you should be getting here as your 5th and 6th items are these, in whichever order you deem appropriate.
Turbo Chemtank - boss engage potential
Randuin's Omen - nice ball of stats and very slot-efficient. Active is good too.
Thornmail - do they have a Tryndamere who's day you wish to ruin?
Spirit Visage - ball of stats and maxes out your CDR with Frozen Heart and runes
Locket of the Iron Solari - maxes out CDR and good aura/active if they are an AoE roflstomp comp
Banshee's Veil - do they have one extremely strong engage spell that will ruin your day if you're hit by it?
Frozen Mallet - are you ahead? do you want to make the enemy cry for mercy? If you have this, nobody escapes. Nobody.

This will just be an unsorted list so do with it as you wish.

Ninja Tabi - if they have close to no AP or CC. Something like Fiora top and Tryndamere jungle with their mid being like Zed or something.
Zephyr - "oops they are all AD so i got Ninja Tabi, but they still have CC" - this replaces BotRK in all likelihood.
Guinsoo's Rageblade - An interesting choice. It was strong when BotRK's build-path was shit, but now that that's fixed, it's less appealing. Still a nice budget replacement for BotRK if you wanna be a bit more AP oriented.
Wit's End - "i picked up Recurve Bow early then realized that if i get BotRK, i will get exploded in 0.2 femtoseconds, so i need defenses." - another good budget replacement for BotRK since the build path fix.

Generally, you don't do well against heavy lane bullies, be they poke bullies like Teemo or trading bullies like Darius or the unholy union of the two like Pantheon.

On the other hand, moderate lane bullies, who aren't that heavy bullies but aren't passive laner either, Riven, Tryndamere, Shyvana and Renekton come to mind, you do well against. You can trade decently with them and you can really punish them if they make a mistake.

Naturally you can do really well vs weak laners due to their nature of being weak in the lane (go figure).

One outlier to this is Nasus who you still lose to due to it just being a lopsided matchup: you can't do much to him until lvl 6, when you generally need to bully out Nasus, and you naturally push with your passive allowing him to farm under turret. After 6 you still can't do much to him since he'll have his ult, and he can capitalize on your lack of disengage by just casting Wither on you and letting his jungler to carve you up.
Just avoid this matchup if possible or call for frequent ganks if you end up in it.

That all said, as long as you can farm up a Sheen around your hitting lvl 6 and not die, you should be fine with any matchup. Your Q is a really good tool for farming from afar if it comes to that.