Im not gonna write out a books worth of stuff on matchups but I can give some general tips:


Against Bruiser and Tanks farm Grasp as much as humanly possible. You bully pretty much every melee champ in the game by Q Spamming and Breaking Barrels, but a lot of champs can beat you in the all in early game so make sure you don't over-commit.


Assassins are also easy to farm Grasp off of, but by level 3 most can kill you easily in an all in. Play smart with barrels, and play it smart. Punish their mistakes with Barrel and Q, and go for the all in when you can ensure the kill.


If you're laning against a Mage, most will prefer to play outside of Q range. Focus on farming and looking for cheeky barrels. With your passive, ult, and the slow/haste from barrels, GP can actually run down a lot of mages if you can get them low enough.


Laning against an ADC like Lucian or Quinn is likely the worst case scenario for GP. For the most part, play it similar to mages. Start Doran's Shield if you need it, freeze the lane, and look to setup ganks.


Always be on the lookout for ult plays whether its to help your bot win a 2v2, help your jungler if they're being invaded, etc. GP's global presence is one of his greatest strengths.


Your late game and teamfighting is very strong compared to most characters. Look to poke with barrels, Ult engages, and never be afraid to run into melee range to cut someone down