Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Okay, so this being my first guide, I'm going to do my best to explain this in text.
This IS a hit or miss guide. I have honestly not lost a game as Morgana since beginning to use this build. I will be writing this guide based around winning (assumable).
Summoner Spells - Clarity - This should only be used if you are absolutely out of mana or you are in a teamfight and someone is extremely low on mana. Use it sparingly. Your runes should be able to easily be able to generate enough mana to farm easily.
Ghost - I use this mainly to chase someone and hit them with a snare, as simple as that. Also a great escape mechanic, I prefer this over flash because I can get in and out, not either or.
Early Game - First things first. You want mid with this build, and you want to level your pool up fast. Last hit minions at all possible times, but don't be phased if you are against a better early game farmer than you, you'll be catching up very soon. Unless the other team is playing extremely aggresively, I will stay in my lane until I have enough gold to finish my boots and get my Mejai's. I don't attempt to gank until then, your strategy may differ. At this point you should be a gank machine. Unless the other mid stayed in the lane, you SHOULD be atleast a level higher than him, maybe even more. I have not yet been outlevelled while using this strategy. Don't be afraid to chase or dive someone if you have your combo up, you should be able to get in and out fast enough, or if not, just ghost in. You should have 6-10 stacks on your Mejai's very soon.
Mid Game - At this point, if you have 6-10 stacks on your Mejai's, it probably means that you can go buy your Zhonya's, or atleast both parts of it. If that is the case, it should be game over. Some games will go slowly, with the other team playing extremely slow and defensive. If anyone on the other team is out of place or makes a mistake, you have to be ready to be there and to gank them, don't go alone, because the odds are just as well that they are bait, not just someone making a mistake. Push turrets when possible. Shield up yourself and teammates whenever needed, and just hammer people with your level advantage and the AP from the stacks you have. Buy an Archangel's if needed, if not, go straight to Rylai's.
Late Game - If you make it to late game, the team you are playing against is very good, or you aren't doing this right. Buy that Rylai's if you havn't already, and get that void staff. You will need the Magic Penn at this point. If you lose stacks in a teamfight, don't be discouraged, you should play a little more conservatively and work to get them back ASAP. Buy either a Banshee's Veil or a Guardian Angel depending on how the other team is built.
Again, this build is built to win games FAST. You can grab blue buff if you like, but I actually prefer letting someone else have it over me, because I have enough mana, and if I have a good accompanying DPS then I let them have it. Not sure much else to say. Thanks for reading this if you decided to.