Hello guys this guide will be about the fabulus MAGIC JAYCE.
It's a build that i came up with and, even if i had some doubts at the beginning, it can really work, hope you enjoy.

At first you can say easily: "Wtf? AP Jayce is worthless" And it's actually true, just one ability that scales with ap and it's 100% over 4 sec, definitly not good is a compliment.
B U T
I didn't say AP, I said MAGIC ("Do you belive in magic?") so that's what tought might work: Magic Penetration- Tanky Jayce.
Why? Because it's complitely reliant on FLAT DAMAGE, so you only have to build penetration to make it work. Tanky is because you will have to dive deep in the enemy backline to kill or render useless the carries.
How? Well you have tons of underrated magic damage aoe that comes from your W Lightning Field (Remember that ranged dont grow magic resist with level and building mr for first/second item on adc means you just dont deal damage), also your E Thundering Blow deals Magic Damage and your first base after transforming into Hammer Form deals some very good Magic Damage, which (trust me) is enough to kill a not-so-fed adc.
So does this mean Cannon Form is useless in this build? No, your first base shreds armor and magic resist % form the opponent, which is very good expecially late game, but is also very usefull early to mid, and the first spell you max is W, which not only gives you 3 max speed base, but also resets your autoattack, meaning you have very fast tower killing potential and the reason you build Wits End is that at max rank it's cooldown is just 5 seconds, with all the CDR you build is 3 seconds,so the autoattacks will also deal very heavy magic damage. Because you will have to be in very close range with the enemy carry, both your E Acceleration Gate and your Q in Hammer Form To The Skies! (but also your passive which gives movement speed and ignores unit collisions) help a lot to cover and mantain the distance.
Finally the only spell that is pretty much useless (except for some little damage early on) is your Q in Cannon Form Shock Blast.

Early game you have very underrated damage that can really make the difference because who plays ap Jayce? So no one knows the hidden power of maxing W first, and they will just commit to early trades that they think they can win, and just bump into your W dealing tons of damage.
You will have a little decrease of power before taking Sunfire, expecially if you swap it with a MR item, but once you get both of them completed with boots it's just funny watching the enemies carries die to unexpected JOHN CENA, no unexpected Lightning Field dealing tons of damage while they're slowed by TO THE SKIES! and you're moving so fast in the Accelleration Gate, with the base shreadind MR and dealing very heavy damage, before getting dunked by your E Thundering Blow that deals 20% of max hp (obviusly in Magic Damage) and these damage will most likely be as scary as True Damage for all the Magic Penetration you have.
Later in the game you will start to fall off, but you can still be annoyng as a hybrid tank (for example taking Zhonya can be good if they burst you as soon as you jump in)and force them into building magic resist. This is the reason why i put in the options auras items, you want to support your team. Even in the late game if you manage to throw the enemy adc back into your team by jumping on him, flashing behin him and pressing E, you just won a fight unless they have other hard carry fed.
Anyways you still are a very strong splittpusher because or the combo Sunfire- Lightning Field for creep waves and Hyper Charge for turrets, while looking always at the map to tp into the enemy team.

Magic Jayce is a Hybrid Magic Penetration-Tanky bruiser that can jump and scare away the enemy carry, it is fairly easy to play and it's an optimus way to surprise your opponents, althuogh he has some weaknesses like the lack of range and the ***ence of poke.
Whrite a comment if you want to let me know where i can improve or if you want to tell me that you like it (or if you don't like it and why).
Hope You Enjoyed