Originally published at: Revised Wizard and Chaos Mage Kits — Errata — Advanced Old School Revival — OSR+
The Wizard and Chaos Mage kits have been revised to make them more versatile.
Previously, Wizards could scribe scrolls from a school of magic they chose at character creation. While this is still the case, Wizards can now replace all the spells they know with different spells upon resting, by spending 1 MP per spell to replace before resting. This is a callback to the Vancian wizard class in other traditional RPGs, where some spellcasters memorized spells and could choose new ones as they adventured.
You are a living font of knowledge: before you rest, you may spend 1 MP to replace any spell you've learned with a different spell of your choosing. You know the new spells until you choose to replace them the next time you rest. When you adopt this kit, choose a school of magic. You may spend a consumable supply to scribe a scroll that contains a spell from the chosen school of magic. It takes an hour to scribe a scroll, and anyone who reads your scrolls can cast the spell contained therein. You may choose to make a scroll indecipherable except to those with an Arcana skill you know. The reader of the scroll must expend MP to cast the spell at the time the scroll is read, and the scroll is consumed after the spell is cast. Spells cast from your chosen school explode on a 5 or 6.
Similarly, the Chaos Mage kit has been revised for utility. Instead of a chaos surge occurring unless the player rolls exactly a clean success, it now occurs depending on how powerful is the spell they've cast, based on a "probability die."
You experiment with raw, primordial magic, which is as unpredictable as it is powerful. You may choose to cast any spell you have not learned, but if you do, roll a Probability Die to determine if a chaos surge occurs. If you spent 1 MP to cast the spell, the surge occurs on a 1 or 2; if you spent 2 MP, on 1, 2, or 3; if you spent 3, on a 1, 2, 3, or 4. The chaos surge affects an encounter space, as determined by the GM. Roll a d6: on a 1, there is collateral damage; on a 2, your spell has unintended targets; on a 3, something is gained and something is lost; on a 4, there is a transformation or reversal; on a 5, the spell is out of control; on a 6, the spell costs twice as much to cast. Probability spell checks explode on a 5 or a 6.
The intent of this revision is to make the Chaos Mage's central feature (plucking spells out of thin air with abandon) a little more enjoyable for the player.