Welcome to my Gangplank Crit guide. Please check out my Crit montage, although the thumbnail is ugly as f.

https://www.youtube.com/watch?v=vs6z-srGA3Q Play Video /league-of-legends/champion/gangplank-30

http://www.surrenderat20.net/2015/05/red-post-collection-gp-and-mf-on.html

I'll probably update this guide even though it has only been a month after I created this ;^;

*Note* - These crits are on minions. But if you can do 2000 to a minion, you can sure do 1000 damage to a squishy with ONE Parrrley

http://postimg.org/image/jlpi415zd
http://postimg.org/image/nmepkj21p/
http://postimg.org/image/ngsw6lp55
http://postimg.org/image/hdbbmoyvd
http://postimg.org/image/t3p942rnt
http://postimg.org/image/cl1ib947d

PROS

-Fun
-Squishy Killer
-You deal a decent amount of magic damage thanks to your passive, shiv and ult (about 37%) http://champion.gg/champion/Gangplank
-Free Assists
-Safe Laning Phase (All you need is farm during laning phase)
-Insane Crits
-2nd ADC
-Easy to play
-Snowball
-Pirate

CONS

-Countered by Armor
-Low CC
-Low AoE (Low multikill potential. You'll probably score double kills 90% of your games and some triples maybe 10%)
-Spellshields counters him
-Low Mobility (no dashes)

Pros

One extra item slot
-A lot more AD (If you get a offensive item) = Insane Crits!
-A lot more Defense (If you get a defensive item)
-You still move faster than most champions with boots.
-The Parrrley bonus gold, Avarice Blade, Cannon Barrage assists allow you to achieve full build about the same time as other players.
-Great dueling (you don't need to buy boots + your bonus gold and assists)

Cons

-Can't attack the back effective because he'll get focused. Instead, look for an opening to attack the carry with your Parrrley while peeling for your carry. Even if you don't kill them, you'll chunk half their hp or more (even if you don't crit sometimes) and put them out of the fight. They'll be zone from the threat of your Parrrley and Cannon Barrage
-Not as fun if you like to go fast.
-No Tenacity/ Ninja Tabi
-Can't go 450-490 Movement speed, instead around 410-430
-Harder to escape + chase, but shouldn't be too much of a problem thanks to Remove Scurvy
-Slightly harder to Parrrley the back line (in exchange for adding a ton of AD or defense. However, your Trinity Force will get you moving in teamfights after a Parrrley and each Cannon Barrage tick)

Why no Boots?

http://postimg.org/image/v89maxi6t/

In this picture, I have Rank 3 Raise Moral Active and Statikk Shiv and Trinity Force without Boots. Which gives me 436 movement speed, I don't need 45 more movement speed, so I can get another item. AND I get a lot of money, (900 - 1300) per game thanks to my Parrrley. Without spending the gold on movement speed, I can use it on offensive and defensive stats which will ultimately get me more money because of kills. I will also just be plain strong. In that picture, Nidalee says I did 1.2k Crit (because of crit shiv and crit Infinity Edge and crit Trinity Force). I've done more. I've ONE SHOTTED champions (although very rarely and with Sword of the Occult), 100 - 0. With one Parrrley. In my montage, you'll see the crits.

*When getting ONE movement speed item ( Trinity Force or Statikk Shiv) and having a rank 5 Raise Morale (inactive), you'll still have about the same movement speed as most champions with boots.

My Build: I'll explain more about this later. My build is VERY expensive because you are spending an extra 2500 gold than most builds because you aren't building boots. But thanks to your Parrrley, free assists from [Cannon Barrage]], and additional stats most champions won't have because of their Boots, you will be able to afford all of these items (+ elixirs and wards)

Ignite - To snowball harder
Flash - Flash

Teleport - Map presence, but your ult is good enough. I feel ignite is better because you gotta snowball. Take this if you can't kill your top laner or if your team will need you.
Exhaust - I just like to Q and ignite for a kill.
Smite Top - I don't see any use for it besides the item that gives Armor pen, CDR, and AD. But...it's not worth the summoner.

These Items are for Gangplank to enhance his crits and gameplay. MAKE SURE YOU CHECK OUT THE NOTES FOR THE ITEM BUILDS.

Early Items

Crystalline Flask - Helps with mana problems early game and sustains you. Farming with Parrrley gives you some mana problems and this helps you. Gangplank falls off without items so this really helps you survive until you get those items.
Avarice Blade - Builds into Statik Shiv and gives you extra gold for those items.
Sheen (CORE) - Parrrley applies it and it gives better stronger crits.

Core
Trinity Force (CORE) - Stronger Parrrleys, Parrrley applies rage so in addition to your passive, you can really catch up to people and autoing them. The movement speed from this item is what enables you to not build Boots. This is an expensive item but thanks to your Parrrley and avarice blade, you should easily be able to afford it. You can replace this with Iceborn Gauntlet if you're losing.
Statikk Shiv (CORE) - Q applies it and gives you crit chance and the lightning can crit. Gives you movement speed which is key for this build. Helps you with trades and helps apply those passive stacks thanks to the attack speed. This actually helps you with your mana problems too because if the lightning kills a target, you get mana back (you are refunded up to 200% of the mana used) plus you get additional gold.

AD ITEMS

Bloodthirster - Your Parrrley can give you a full shield from this guy. Which means you can safely go in for some autos after your Parrrley, which you would do a lot. Life steal can help you a lot in fights.
Mercurial Scimitar - The Speedbuff can get you in range for a Parrrley and an extra cleanse for when your Remove Scurvy is on CD is wonderful. This is an expensive item, but thanks to Parrrley you are able to afford it. The damage is really good and the MR is good.
Maw of Malmortius - Replacement for Mercurial Scimitar. It gives a shield automatically so it's more reliable. Get this item if you're vsing a AP champion. The AD it gives is good and it helps you more when you are low hp. Thanks to oranges, you can continue being low (not dead) in fights.
Last Whisper (CORE) - Really good item. It's cheap so it lets you build other items right after. For armor pen, I don't see a replacement for this.

DEFENSIVE ITEMS

Frozen Heart (Situational) - Fantastic Item, gives you CDR and armor. The mana is okay, but you shouldn't be going oom after you get Sheen and Statikk Shiv.
Iceborn Gauntlet (Situational) - This is a core item if you substitute Trinity Force for it. Parrrley applies the spellblade on hit effect. Gives armor and mana which are helpful for the laning phase and the AoE Spellblade effect can get you more gold and mana.

Elixir of Wrath - Extra AD and Lifesteal

Vision Ward - Good for baiting. Place it next to a bush as if it was a fail ward and Auto- Parrrley-Auto. Stealth wards and sweepers work fine as well.

I wouldn't get these items...these are up to you.

Randuin's Omen - Helps with sticking onto targets and helps with surviving fights.
Youmuu's Ghostblade - Movement speeds helps with Parrrley and the attack speed helps with duels. The armor pen is nice too. I would only get this on jungle Gangplank (I'll do a guide later)
Frozen Heart - Parrrley applies it and it makes the slow stronger and gives tanky stats and a little AD. However you shouldn't be sticking to enemies like glue, you should be killing them.
Spirit Visage - Stronger Heals, CDR, and tankiness. You can't spam your heals though.
[[Banshee's Veil] - A tankier version of Merculiar Scimitar.
Essence Reaver - Damage, Lifesteal and CDR. The mana gain back isn't too useful for Gangplank. Bloodthirster is better because of the shield.
Ravenous Hydra - I don't like this item that much. Your Parrrley applies it but it doesn't make the cleave stronger. It gives you more gold and HP regen and lifesteal...but I just feel the Bloodthirster is a better item.
Sword of the Occult - Snowball on snowball equals stronger crits? Hurrah. Free stacks from Cannon Barrage and Raise Morale.

Phantom Dancer - You aren't an Autoattack reliant champ. People only get this for the crit chance so it feels like the other stats are wasted. You need the Statikk Shiv to burst while Phantom Dancer gives more sustain damage. I would never get this item.
Ravenous Hydra - The Parrrley doesn't help the cleave.
Boots - Eh :P
Tear of the Goddess/ Muramana - This item is too hard to stack on Gangplank since you need an enemy or a minion to use spam your Q. The mana is also wasted in the late game, you don't need an extra 750 mana. Muramana can you give great crits at around 30 minutes in IF you stay top lane all day, which you shouldn't.
Sunfire Aegis - You aren't going to go in the middle of the teamfight to do that AoE sunfire damage. For jungling it helps with the clear and you're tanky, but for a more AD build, don't go this.

Gangplank can easily get first blood thanks to his passive slows and the short cool down of your Parrrley. Just stand in the top lane push closest to your enemy. Wait for them to facecheck it, and then Auto- Parrrley-Auto. This could get them to 1/3 or 1/2 hp even if you don't crit and even if you don't have flask. Flash to follow them if they flash and continue autoing and Parrrleying while your passive slows down and does some decent damage. Ignite them as they are running away after your final auto. If necessary, take one turret hit if you have enough health to Parrrley (although they should be dead) as long as if they don't have a skill that can stun you under turret. Remember to take a potion (normal HP for more HP regen).

If Gangplank Crits (8% which should give one of your autos or Parrrley a crit in the fight), then you are practically guaranteed to burn a summoner or get a kill.

Of course this has some exceptions, such as Lee Sin who has early dueling potential because of his Sonic Wave and Trundle can survive your trade if he Chomps you.

CRIT REDS - You get those early crits. One Crit can practically win you the lane through lvs 1-3. Can substitute for flat ADS, but I really like crit reds.
ARMOR YELLOWS- For fighting early.
SCALING COOLDOWN REDUCTION GLYPHS - Gives you more Parrrleys and Remove Scurvys. Gives you more ults to clear minion waves. Can substitute for Flat or Scaling MR, but I really like the CDR.
AD Quints - Stronger Autos and Parrrleys. You can replace this with Crit damage, but it's less reliable. Each crit damage quint will give you 25-75 more damage on champions per crit. It isn't reliable in lane however.

Other Viable Runes: Armor Pen, Crit Damage, Flat AD, MR.

Sorcery - CDR=More Parrrley, Remove Scurvy,and Cannon Barrage.
Brute Force - Duh.
Martial Mastery - Duh
Spell Weaving - Stronger Parrrleys.
Executioner - Execute people with Parrrley.
Dangerous Game - Good mastery overall.
Warlord - This mastery is pretty meh. With all the items in my build, it'll give you 20 - 25 AD. But it takes so long to get those AD.
Devastating Strikes - Armor Pen and Magic pen (for passive and ulti)
Havoc - Duh
Why no Frenzy ?
You shouldn't be attacking that much, just get a Q whenever. You'll burst people down before you'll get 3 stacks on this. You can get it instead of a point in Warlord. Depends on the player.

Parrrley First - Mainly for the gold bonus. Gives a little more damage which means a little more crit damage. Too bad it costs extra mana.
Remove Scurvy Second or Last - The heals are pretty good and the cleanse is awesome. I max this last most games, but I take it first if I'm losing. You can leave it at rank 3 and start ranking your E or you cna max it. Remove Scurvy for the CDR and heals.
Raise Morale Second or Last - This skill is better if used for teamfighting rather than yourself so you might want to rank up Raise Morale once you start team fighting a lot. This passive is the key factor for no boots Gangplank, as it gives you bonus movement speed which allows you not to build boots. This gives you strong Parrrleys, you should use Raise Morale before you start comboing.

Passive - Grog Soaked Blade - Grog Soaked Blade is really good early game. This lets you stick onto a lot of champions and helps a little with trades early on. This passive easily can get you kills as they can't escape. Late game, this damage is nothing because it scales off your level.

DO NOT RELY ON THIS TO GET YOU A KILL.
It has 3 ticks, one tick starts after your Parrrley/auto. The next two will do 3 + your champ level. You can see this passive killing an enemy while fighting them, but this rarely gives a kill. Ignite to make sure they die.

Q - Parrrley - This is a ranged auto attack that can crit and apply on hit effects. This is why people build crit items on him. Use this to farm for bonus gold, poke, and execute. In teamfights, use this is safely get a squishy to half health or to kill them.
W - Remove Scurvy - Cleanse and Heals. The Cleanse begins immediately, so it is possible to instacleanse. I recommend not using it if it not necessary just to sustain because it does cost a bit of mana and gives your enemy an opening (if they have CC). There are exceptions for champs that have no little or no threatening CC. Use this in the Mid and late game to sustain against minions if you don't have life steal.
E - Raise Morale - See above.
R - Cannon Barrage - The damage actually isn't bad...if they stay in it. It does maybe a 100 damage per second to everyone for champions in the late game. Mid and Late game you should use this to clear minion waves and thanks to some CDR, it'll be up often. Use this to get a free assist. The ulti applies the rage from trinity force for some reason, it's pretty cool but not that helpful.
Cannon Barrage - Early Game - Use this for for your E-Q-Ignite-R walkaway combo. This ult will burn flashes early game and wonderfully set up ganks for your jungler, along getting you some assists.

Cannon Barrage R - IMPORTANT
This is a global ult, use it whenever you see your jungler come in for a good or a okay gank at any lane to grab an assist, some cs :P, and maybe a kill. A lot of people don't seem to know how to effectively use this ult (in low elo?)