Lane sustain, money stacking, and global pressure.
Creative tools and rule bending
Your first attack after using an ability on champions grants gold and sometimes consumables.
Gain a free stopwatch. Stopwatch has a one time use Stasis active.
You can enter debt to buy items.
+5% Max CDR
+5% Summoner Spell CDR
+5% Item CDR
+20% Potion and Elixir Duration
+22 Ability Power or +13 Attack Damage, Adaptive
Gain cooldown reduction and max cooldown reduction on your ultimate. This is increased further each time you use your ultimate, up to a maximum.
Gain 10% CDR when you reach level 10. Excess CDR becomes AP or AD, Adaptive.
Gangplank is one of the biggest abusers of Kleptomancy thanks to his on-hit [Q]. Klepto will provide you with a ton of sustain/gold and occasionally more AD.
Perfect Timing is a great rune when looking to get an early/cheaper Guardian Angel.
If you find yourself in a tough lane matchup and think you'll need more sustain, take Biscuit Delivery here instead.
The gold earned from Kleptomancy is a great offset to the Lending Fee on Future's Market, allowing you to hit your item power-spikes earlier without major detriment.
If you'd prefer to just earn/save as much gold as possible for big damage items, take Magical Footwear here.
More CDR means more [Q]s which means for Klepto procs which means more gold... You get the idea.
One of GP's most underrated aspects of his kit is his global presence. A few well-placed/timed [R]s in the early game can make or break a lead. More [R]s mean more map presence.
If you're playing into a burst mage mid like Syndra, you can take Nullifying Orb here as a pseudo Hexdrinker.
There is no stat that GP likes more than CDR. His [E] heavily relies on having a lot of CDR because you're going to miss a lot of barrels.
If you intend on stacking to 40% CDR on items alone and think the game will go late, take Gatherin Storm instead.