Hi, I go by MrBlivious, I was bored so I decided to make this guide to share some of my knowledge on how I play Pyke mid, I am currently only silver, with a winrate of 70% in ranked playing Pyke mid, I hope you find this guide helpful, and I am glad you are interested in what I have to share. I can't upload a screenshot of my current ranked Pyke mid stats, but if you really want, you can look me up somewhere to find them.

Pros
-Always ahead in gold
-Insane mobility and stealth
-Great roams
-Can change teamfights drastically
-A lot of outplay potential
-Variety of abilites and uses
-Passive can allow for multiple appearances in teamfights
-Great engage and escape

Cons
-Bad wave management
-Gets proggresively worse and must win early
-Ult can be stopped if one person dodges it
-Very squishy, because you can't build health items
-Late game passive is a lot harder to fully recharge grey health, becomes even squishier to due slower grey health regen

This is how a normal Pyke mid game usually goes, and how I play it. You can invade, but it is risky since you don't have e or w to escape, but if you manage to get first blood its worth. First blood lets you get ahead in your own lane allowing for more roaming. If you don't invade thats perfectly fine, Lv1 try to kill the enemy in lane to get first blood unless it is someone like Sylas, with a champ like that try to get a gank from your jungler so you can roam, or your going to be stuck there with sylas and not be able to do much. If you can get first blood, you can push lane, recall, and get your items, unless you feel unsafe because of the enemy jungler, and just want to recall without risking pushing wave, especially with pyke, it takes longer to push wave with his bad wave clear. If you lose to your enemy laner, try to get your other lanes ahead, even if it means losing turret, because thats half your team, and your able to practically double their gold. Don't kill steal if they have a bounty or if your ult is on cd, only kill steal with ult unless they have a bounty, because it will give you the bounty not your teamate. Also make sure to have good vision, since Pyke is very capable of doing so, I myself do not have very good vision, and to me requires good map awareness which is something I need to work on. I know you want to engage in a teamfight with pyke, but trust me don't, wait for your teamates to engage and try to get those good ults. If the game goes on for too long, try to find someone away from their team and assasinate them.

Duskblade of Draktharr: Don't take any other mythic, Duskblade can regen grey health after a kill, and help you escape after using ult, pretty much the best item for Pyke.
Umbral Glaive: I usually never use this item, but if you are excellent at roaming and have good vision, it can be very useful.
Youmuu's Ghostblade: Take second every game, big lethality powerspike, and great mobility, good to get out of bad situations when w is on cd.
Edge of Night: This item is great if you keep getting hit by that same ability that leads to your death, plus it gives you 73 damage because Pyke passive doesn't let him build health and converts it into damage - 1ad per 14hp - just make sure its up before you try to fight again.
Ravenous Hydra: This item has very high damage, and 10% omnivamp, but a better choice in my opinion is manamune/muramana.
Manamune/Muramana: This item has insane damage, and is sometimes the last item I get because it's damage is so high, another reason to love this item is it gets ult line further up.
Death's Dance: Saves you in most occasions, and pairs really well with the fact that you execute people which gives you health, and throws away that 30% damage you would have taken, usually build third unless at least 3 of them are ap.
Serpent's Fang: Very situational, only build if they have a lot of shields, or enchanter champs.
Maw of Malmortius: Build into ap champs, not much more to say, but its really useful.
Chempunk Chainsword: [/color]Build into matchups with champs that heal a lot, if necessary you can build Executioner's Calling first item if they have a lot of healing.

Mobility Boots: I first started building cdr boots, then switched to these, then went back to cdr boots, these boots are great for roaming and getting back to lane, but I do feel cdr boots are more useful earlier in the game.
Plated Steelcaps: Take into ad comps or champs reliant on aa.
Mercury's Treads: Take into heavy cc and/or ap matchups
Ionian Boots of Lucidity: Best boots on Pyke, if you build them early your ult comes way quicker, and you basically win every fight if you are ahead.
Guardian Angel: If you don't feel safe with that big bounty of yours (assuming you have a big bounty because you read this guide and won every game) then buy this item, but if you can hold it then don't bother, because there is good items you are replacing by buying this, still good though.