Skill Runes are skill-modifying items that are randomly dropped by monsters and used across all classes. They can be attached to each skill like an item, often completely changing the gameplay of each skill.
BOOM video 1056 The lead designer showed off the Teleport skill with a Striking rune, turning the spell into an offensive skill that can destroy enemies. The Skull of Flame skill was modified by the Multistrike Rune, which split the single fireball into multiple splashing attacks, to the crowd's enormous delight.
The Electrocute spell was modified with Multistrike, turning it into a Chain Lightning-esque spell. The Lethality rune added an explosion effect to Electrocute, splattering enemies on contact.
Wilson first took the crowd through the evolution of the current Diablo III skill system.
"We wanted to have more depth to the combat [than Diablo II], so that skill system was hard for us because of that," said Wilson. "The tree also had a lot of unwanted skills, but you had to take them even if you didn't want them."
Wilson also talked about how Diablo II offered skill choices where "1 point is all you ever need, but you can spend 20 points."
"Why is that? It seemed like a lot of opportunities to make mistakes, and there's no respec," he said.
When it comes to the World of Warcraft, Wilson noted that one problem with directly adapting that system to Diablo III is problematic due to the minimal builds available.
"There really is kind of a good path of the talent tree, and that's desirable of a game that has so many different ways to play it for balancing, but for us that's not as much of a concern."
Wilson eventually explained various skill trees in what he called the team's "Crazytown." Various skill designs Skill Cards, Skill Ring, and a Skill Wheel.
"I honestly don't remember what this did," said Wilson on the Skill Wheel. "I think there was some kind of spinning involved."
Wilson then revealed a diagram of an incredibly complicated Horadric Cube-styled Skill tree, to which the crowd roared in laughter.
The lead designer then elaborated on how the team reached the current scheme, including two ideas they wanted to incorporate into the system: randomly dropped skills, and skill modification. Thus, Skill Runes.