Back at BlizzCon in 2008, Blizzard unveiled a system for Diablo III named Skill Runes, which would allow players to customise their spells and abilities. A lot can change at Blizzard in three years, and so the developer has now revealed the latest iteration of the system--Skillstones.

Runestones will change the way a skill operates, adding secondary effect such as stunning or an increased area-of-effect radius. They'll come in five different colours, each affecting every skill in a different way. Runestones will also have power ranks, applying more intense effects the more powerful the stone is.

A Golden Runestone applied to the Sweeping Wind skill, for example, will make it increase the monk's Spirit regeneration. An Obsidian Runestone, however, would cause Sweeping Wind to also create a whirlwind around the monk, damaging enemies who touch it.

Runestones will apply different effects to different skills, too. While an Obsidian Runestone applied to the demon hunter's Cluster Arrow skill will make it rain grenades, on the witch doctor's Acid Cloud it'll spawn slimes to attack nearby enemies.

The initial Skill Runes system did sound a little more straightforward, with each rune seeming to applying a similar effect to every skill. 'Multistrike,' for instance, would always make it affect multiple targets, while 'Lethality' would simply amp up the damage in some way. Still, if you can count on anyone to rework a system until it's perfect, it's Blizzard.

The developer also recently revealed Diablo 3's Follower system, a nifty replacement for the mercenaries from previous Diablo games.

Blizzard expects Diablo 3 will enter external testing in the third quarter of this year. Company president Mike Morhaime said earlier this month that the development team is "working hard to try and launch Diablo III this year," but this certainly should not be mistaken for an official release window. Activision has said that if no Blizzard games this year, we should see two in 2012. The other's expected to be StarCraft II: Heart of the Swarm.