The Dungeon Master's Guide lists numerous variant rules. The ones used in the campaign are listed here. Slight changes to the variants are listed in italics.

• The Surprise Round - the first round of combat is always a surprise round, with partial actions only.
• Defense Roll - Against any attack, before the attack is rolled, a player may choose to subtract 10 from his AC and add 1d20 (New AC = AC - 10 + 1d20). However, a roll of 20 is always rerolled.
• Critical Miss - A roll of 1 is a critical miss threat. Roll again, and if another miss comes up, the attacker fumbles. The exact effect of this fumble is up to the DM, but usually involves a loss of a turn.
• Clobbered - if a defender takes over 1/2 her current hit points in a single blow, she becomes clobbered. A clobbered defender can only take a partial action in her next round, then ceases to be clobbered.
• Critical Success or Failure - skill and ability checks are subject to critical successes and failures just as attacks are. The exact effects of these criticals are up to the DM.
• Spell Roll - A spellcaster may choose, before any saving throws are rolled, to roll a d20 instead of automatically adding 10 to his spell DC (New DC = DC - 10 + 1d20). However, a roll of 20 is always rerolled.
• Summoning Individual Monsters - as described in the DMG.

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