Adventures in Theia
Magic World is a game primarily based on Chaosium’s old Stormbringer/Elric!, brought up to date to be compatible with Basic Roleplaying (aka. BRP). I strongly encourage you to support Chaosium by purchasing the Magic World rules from their webstore.
For your convenience you can download and reference this bookmarked, copy of Magic World, that is also bundled with the Advanced Sorcerery supplement. Advanced Sorcery includes a variety of new sorcery spells, rules for High level skills, Herbalism, Summoning, Necromancy, Deep Magic and more.
The house rules integrated into the copy, corrects some flaws and idiosyncrasies in the weapons and armor tables and cleans up some of the remaining errata that Chaosium never got around to fixing.