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.
So u want to get raise morale first, stay by the inhibitor corresponding the lane you are going to be in and use raise morale on one of the melee creeps. walk up with the creeps and the cooldown for raise morale comes back and use it again to kill another melee creep. This strategy is good to make sure your opponent is always going to be underleveled compared to you and can equal kills later on.
As soon as you get enough gold to get 2 avarice blades teleport back to base and buy them so the passive works in your favor earlier. After that get boots, either swiftness or berserker, or merc treads if there is alot of CC on the opposing team.
The whole point of this build is to get a CRAZY amount of gold, with 3 avarice blades + last hitting with parrrley you can easily afford the rest of the build.
Make sure you have the map awareness to use your ult effectively when your team needs it.
After you get the first phantom dancer you will have 6 items, when you get enough money for another phantom then sell an avarice blade and buy it. THe increased movement speed, crit chance, and attack speed are all good things on gangplank.
Hopefully by end game you will easily be able to crit most of the time and parrrley should be critting near the 1k mark.