When it was first explained to me way back in 2008, the power-enhancing rune system of Diablo III sounded like it would lead to countless permutations of every skill and spell in the game. Now it's only five, but they're still pretty spectacular.
This slimmed-down runestone system made its debut at last year's BlizzCon. Rather than messing about with damage runes, multi-shot runes, frog runes, and the like, Blizzard slimmed things down to a more manageable five, color coded for convenience. Affixing these crimson, alabaster, obsidian, indigo, and golden runes to your powers dramatically effects how they perform.
Take the Demon Hunter's Cluster Arrow skill, seen above. Adding a crimson runestone to the skill merely increases the damage done. A golden rune transforms the explosions into shadow creatures, leeching life from enemies and returning it to the Demon Hunter. Alabaster adds a stun effect, obsidian rains down grenades, and indigo fires enemy-seeking missiles.
Runestones come in different power ranks as well, with their special effects becoming more pronounced as the power level increases.
For a closer look at this simple-yet-effective way of mixing up skills and spells, check out the Diablo III runestone page.
Ray of Frost