I would recommend to go Kleptomancy only against meele Champions, because you will be able to get it more often. You can also take it against ranged Champions, but you won't get it as often, which makes it very useless.

When playing against a ranged Champion, it's better to go Grasp of the Undying, because you still deal damange but you have the advantage, that you are tankier.

"Every few seconds, Gangplank's melee strike will set his opponent on fire."

Gangplanks Passive has "2 Parts":

The first Part:
Gangplank's next basic attack burns the target, dealing 55 - 225 (based on level) (+ 100% bonus AD) bonus Hybrid penetration icon true damage over 2.5 seconds, with each tick occurring every 0.25 seconds. Turrets receive 50% reduced damage.

The second Part:
If Gangplank successfully hits a target with Trial by Fire, he Trial by Fire 2 gains 30% bonus movement speed for 2 seconds. Destroying a Powder Keg Powder Keg instantly readies Trial by Fire and grants its bonus movement speed.

STATIC COOLDOWN: 15

Gangplank's Passive is one of the most important, but also one of the most ignored Ability in his Kit. It is mostly use to win trades or to run from dangerous situations.

"Shoots target, plundering Gold for each enemy unit killed."

Gangplanks Q has a Active and a Passive:

Active:
Gangplank shoots the target enemy with his pistol, dealing physical damage and applying on-hit effects. Parrrley can Critical strike icon critically strike, dealing 100% AD bonus physical damage.

Passive:
If Parrrley kills its target, Gangplank plunders gold and Silver Serpents Silver Serpents, the latter of which can be spent to upgrade Cannon Barrage Cannon Barrage.

TARGET RANGE: 625
COST: 60 / 55 / 50 / 45 / 40
MANA COOLDOWN: 5

Gangplank's Q is used to poke or to farm Minions, which are not in range.

"Eats citrus to cure crowd control effects and restore Health."

Active:
Gangplank consumes a large quantity of citrus fruit, curing all disabling effects and healing him for 50/75/100/125/150 (+90% Ability Power) + 15% of his missing Health.

COST: 80 / 90 / 100 / 110 / 120
MANA COOLDOWN: 22 / 20 / 18 / 16 / 14

Gangplank's W is used when getting CC'd or when being low life.

"Gangplank uncovers a powder keg at target location. If he attacks it, it explodes, spreading the attack's damage to enemies in the area, slowing them."

Gangplanks E has a Active and a Passive:

Active:
Gangplank places a Powder Keg at the target location for 25 seconds, which connects to other nearby Powder Kegs.

Gangplank and his enemies can attack the Powder Keg with their basic attacks, dealing 1 damage per hit. Gangplank may also shoot the barrel with Parrrley. If Gangplank scores the killing blow, it explodes, also triggering a chain reaction that explodes nearby connected kegs. If killed by an enemy, the keg is safely dismantled.

An exploding keg deals the attack's damage to all nearby enemies, plus bonus damage against champions, ignoring 40% of their armor, as well as Slow icon slowing them for 2 seconds. Enemies can only be damaged once.

Passive:
Gangplank stores a charge of Powder Keg periodically, up to a maximum of 3 stored at once.

TARGET RANGE: 1000
COST: 1 CHARGE
RECHARGE TIME: 18 / 16 / 14 / 12 / 10

Gangplank's Kegs are his damage source, they are used to trade, kill and slow.

"Gangplank signals his ship to bombard an area, slowing and damaging enemies."

Active:
Gangplank signals his ship off-shore to fire upon the target area for 8 seconds, calling down 12 waves of cannonballs in clusters of 3 every 2 seconds, and Sight icon revealing it for the duration. Each wave deals magic damage to all enemies within the area and Slow icon slows them by 30% for 0.5 seconds.

Gangplank can purchase upgrades for his ship in the store at the cost of 500 Silver Serpents Silver Serpents each, which improve Cannon Barrage:

DEATH'S DAUGHTER: An initial cannonball lands in the center of the barrage, dealing a cluster's worth of Hybrid penetration icon true damage to all enemies it hits and Slow icon slowing them by 60% for 1.5 seconds.

RAISE MORALE: The barrage grants allies 30% bonus movement speed while they are inside the area, persisting for 2 seconds after leaving it.

FIRE AT WILL: Cannon Barrage fires 6 additional waves over its duration.

Gangplank's Ultimate is used to initiate Teamfights or to pick up Kills/Assists from the entire map.

look above for any matchup