I haven't had the chance to play yet this patch but it doesn't sound that bad on paper, though I feel like if you are snowballing and wanna go for a crit mythic instead of Prowler's or Trinity you might as well go for Galeforce just to get an additional damaging ability/escape tool. Shieldbow's added sustain and survivability is nice but with the way Riot's pushing him to be a full-crit oneshot AD mage I think it's better to go for utility or damage rather than sustain, leave the assisting part to your teammates.

I take DH and that's all the validation I need. Grasp and First Strike might be better but GP can work with most runes if you're comfortable with him.

tbh ive only ever used it once or twice and that was years ago, didnt know it doesnt work anymore so ill remove it from the guide, ty.

You can still take it but it's nowhere near as strong as it used to be, Dark Harvest and Fleet Footwork will most likely be the optimal picks moving forward if my assumptions are correct.

1. I don't follow pro players, not sure where you're getting the knowledge that I don't "respect their choices".

2. The item options are displayed just as that, options, Trinity Force is the best mythic for sure and I myself take it in I would say 95% of my games but if you think I'm not displaying that clearly enough in the guide I shall fix that.

3. Galeforce and Prowler's Claw aren't "funny trolling, smurfing, or just garbage", again, I take Trinity in most games but I do believe that the two other options mentioned here are good situationally/fit better in specific builds.

Thanks for the comment and have a nice day.

Thanks bro.

Play early game like you would play with AD, be aggressive and look for kills.
In mid game your damage output won't be as high as with AD so your main goal is to just help teammates with ult while farming sidelanes.
When you reach late game you should be looking to land the center of your ultimate on squishy or CC'd targets.
- If the enemy has baron buff and are sieging a lane with a large minion wave then your best bet is to ult it unless your teammates have sufficient waveclear, AP GP's barrels don't deal much damage to buffed minions.

Also remember that AP is not necessarily meant for every game, if you find it hard to carry with then only pick it in the following two scenarios:
1. Team is lacking magic damage.
2. When the enemy team has several high attack range/high attack speed characters who can disarm your barrels easily, this way you can at least deal damage to them with your ultimate.

I'm glad you enjoy it!

It's a hard question to answer because GP can have a lot of variety in what he takes every game.
If you want the most basic answer then I guess it would be this;

AD GP:
Grasp/Conqueror against melee. (I only suggest conq if you're really familiar with the matchup.)
Fleet against ranged.

AP GP:
Dark Harvest against melee.
Arcane Comet against ranged.

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But of course there's some variations, for example if you're against Teemo you shouldn't take Fleet because he is very easy to kill early on with Grasp, if you're against Neeko/LeBlanc then Dark Harvest is pretty good no matter what build you're going because you can stack the rune against their clones.
It all just depends on what you feel like works for you in each matchup.
As far as just simplifying what runes you could take in each lane I'd advise with this:

TOP: Grasp, Fleet, DH, Comet, Conq
JUNGLE: Fleet, DH
MID: Grasp, Fleet, DH, Comet, Conq
BOTTOM: Grasp, Fleet, Comet, Glacial
SUPPORT: Grasp, Fleet, DH, Comet, Glacial
(But in botlane you would most of the time just take Fleet because it's rare to get a matchup that you can easily poke as GP.)

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Hope this helps!