A Codex is a Mythic spell (or collection of Mythic spells) that has been stored in written form. A spell on a Codex can be used only once. The writing vanishes from the Codex when the spell is activated. Using a Codex is basically like casting a spell.

The price of a Codex is equal to the level of the spell × the creator’s caster level × 25 gp. If the Codex has a material component cost, it is added to the base price.

Activation: To activate a Codex, a spellcaster must read the spell written on it. This involves several steps and conditions.

Decipher the Writing: The writing on a Codex must be deciphered before a character can use it or know exactly what spell it contains. This requires a read magic spell or a successful Spellcraft check (DC 20 + spell level). Deciphering a Codex is a full-round action.
Deciphering a Codex to determine its contents does not activate its magic unless it is a specially prepared cursed Codex. A character can decipher the writing on a in a Codex advance so that she can proceed directly to the next step when the time comes to use the Codex

Activate the Spell: Activating a Codex requires reading the spell from the Codex. The character must be able to see and read the writing on the Codex. Activating a Codex spell requires no material components or focus. (The creator of the Codex provided these when scribing the Codex.) Note that some spells are effective only when cast on an item or items. In such a case, the Codex user must provide the item when activating the spell. Activating a Codex spell is subject to disruption just as casting a normally prepared spell would be. Using a Codex is like casting a spell for purposes of arcane spell failure chance.
To have any chance of activating a Codex spell, the Codex user must meet the following requirements.

• The spell must be of the correct type (arcane or divine). Arcane spellcasters (wizards, sorcerers, and bards) can only use scrolls containing arcane spells, and divine spellcasters (clerics, druids, paladins, and rangers) can only use scrolls containing divine spells. (The type of scroll a character creates is also determined by his class.)
• The user must have the spell on her class list.
• The user must have the requisite ability score.

If the user meets all the requirements noted above, and her caster level is at least equal to the spell’s caster level, she can automatically activate the spell without a check. If she meets all three requirements but her own caster level is lower than the Codex spell’s caster level, then she has to make a caster level check (DC = Codex caster level + 1) to cast the spell successfully. If she fails, she must make a DC 10 Wisdom check to avoid a Codex mishap. A natural roll of 1 always fails, whatever the modifiers. Activating a Codex is a standard action (or the spell’s casting time, whichever is longer) and it provokes attacks of opportunity exactly as casting a spell does. If the caster level check fails but no mishap occurs, the Codex is not expended.

Determine Effect: A spell successfully activated from a Codex works exactly like a spell prepared and cast the normal way. Assume the Codex spell’s caster level is always the minimum level required to cast the spell for the character who scribed the Codex, unless the scriber specifically desired otherwise.
The writing for an activated spell disappears from the Codex as the spell is cast.
Codex Mishaps: When a mishap occurs, the spell on the Codex has a reversed or harmful effect. Possible mishaps are given below.

• A surge of uncontrolled magical energy deals 1d10 points of damage per spell level to the Codex user.
• Spell strikes the Codex user or an ally instead of the intended target, or a random target nearby if the Codex user was the intended recipient.
• Spell takes effect at some random location within spell range.
• Spell’s effect on the target is contrary to the spell’s normal effect.
• The Codex user suffers some minor but bizarre effect related to the spell in some way. Most such effects should last only as long as the original spell’s duration, or 2d10 minutes for instantaneous spells.
• Some innocuous item or items appear in the spell’s area.
• Spell has delayed effect. Sometime within the next 1d12 hours, the spell activates. If the Codex was the intended recipient, the spell takes effect normally. If the user was not the intended recipient, the spell goes off in the general direction of the original recipient or target, up to the spell’s maximum range, if the target has moved away.