Your spells can have a chance to deal double damage - this is called a spell critical. The damage number on the screen is shown with a larger font when spell critical is scored.
Each damage type has its own chance and the base chance for each type to do double damage is 0%. Magical Training, a feat automatically granted to Artificers, Clerics, Druids, Favored Souls, Sorcerers, Warlocks, and Wizards increases the chance by 5% for all damage types. Class enhancements, feats, Spell Lore items, Epic Destinies, and other effects can further increase your chances to score a critical hit but most of them are selective with the damage types.
Critical hits dealt by the spell are rolled each time a damage effect is applied rather than only when the spell is cast. For Fireball, spell critical is rolled and applied per enemy within the area of effect. For Magic Missile, spell critical is rolled and applied per tick of damage.
Spell criticals are applied only on straight spell damage to your enemy HP (or healing on your ally). Your Jump buff doesn't crit and give greater bonus to your skill. Your Energy Drain doesn't crit and give 6 negative levels instead of 4.
Increasing spell critical chance
- Magical Training +5%
- Mental Toughness +1%
- Improved Mental Toughness +1%
- Epic Mental Toughness +1%
- Energy Criticals 3% each up to 9%
- Chaos Domain 3%
- Offhand Versatility: automatic for 5 seconds after a vorpal hit
- Divine Crusader: Interrogation 1%
- Divine Crusader: Empyrean Magic 1% per stack, stacks up to 10 times
- Spell Lore enchantment
Increasing spell critical damage
Spell criticals usually deal double damage, or +100% extra damage. Few abilities exist that can increase this extra damage.