Armed with wit, charm, and his signature transforming hammer, Jayce lives to protect his native Piltover. Long before his nation called him a hero, however, he was a promising young inventor. When Piltover commissioned him to study a rare arcane crystal, Jayce discovered it could be used as a vast energy source. Eager to make a name for himself, he began developing a device to harness its power. Word of the crystal’s potential reached beyond the borders of Piltover. Viktor, the machine-augmented scientist from Zaun, brought Jayce an offer - together, they could use the crystal to advance his “glorious evolution,” a vision of humanity fused with technology. Jayce refused, but the Zaunite had no intention of leaving empty handed. He effortlessly blasted Jayce aside and seized the crystal, incinerating the lab's meager security force as he left for Zaun. Jayce implored the Piltover government to respond, but the officials refused to support an act of aggression. He decided to act alone, realizing that if no one struck back, Piltover would never be safe.

Jayce returned to the lab to prepare for his attack. After intense research, development, and hands-on testing, he emerged with his crowning achievement - the Mercury Hammer. Weapon in hand, Jayce marched to Zaun and began his one-man assault. Viktor's acolytes rushed to stop him, but Jayce smashed them aside, fighting his way into the heart of the lab. Inside, Jayce saw the horrifying brilliance of Viktor’s creations, all powered by the energy of the arcane crystal. He realized that his only option was to destroy the power source, but Viktor stood in his way. Though their clash left both scientists heavily wounded, Jayce managed a desperate strike at the crystal. He shattered it and escaped as Viktor’s machines erupted in flames. When he returned home, exhausted but victorious, the citizens of Piltover hailed Jayce as a hero. He reveled in the adoration, but knew that his actions had drawn the attention of dangerous enemies. Now devoted to the defense of his people, Jayce is Piltover's best hope for a bright future.

"Trust me: if we're smart, Piltover can stand strong against any threat. Hey, I'm living proof." - Jayce

Note that for marks you can get Armour penetration instead of attack damage too. This is the standard rune page that I commonly use for my ad carries and as always, doesnt have to be followed

JAYCE COMBOs

In cannon form: Q > E
The acceleration gate will give the extra burst that can easily take down 1/4 or more of enemy champion. It takes some practice to pull the combo off but it shouldnt take too much of your time.

In hammer form: Q > E
Note that before you hit E, its best to be ahead of the enemy champion as that will send them flying backwards.

Jayce's Passive.

Each time you transform from Hammer to Cannon mode and vice versa, you avoid unit collision. This is useful for ganks as you can immediately change to hammer form, walk infront of the enemy and give him a good knockback.

Farming

Farming is a breeze for Jayce. Being able to swich from Hammer and Cannon form plus the mana regen from your W. You should be able to easily outfarm you opponents.
Use cannon form when you're low on health and poking the enemy.
Use hammer form when you're low on mana.

FLASH This is a commonly used spell for almost every champion you're playing. It can help you get out of ganks or catch up to enemy champions...
An alternative for FLASH would be GHOST. On top of you're passive plus acceleration gate, unless they exhaust you, you'll probably get out of most ganks~~~

Pros.
-Extremely good 2v1 laner.
-Able to deal large amounts of damage early game.
-Good chasing and escaping skills.
-If used correctly, will have an infinite mana supply early game

Cons.
-Cannon Form range is pretty low.
-Fairly squishly late game.

Jayce's isn't a jungler

I don't understand why some people still try to jungle with jayce. HE IS NOT A JUNGLER