Critical Hits

Chromanexus uses the variant critical hits rule, "Add Max Damage". Normally, when a creature makes an attack roll and critically hits on the attack, they roll twice as many damage die as they normally do.
Under this rule, when a creature critically hits, they roll normally then additionally add the maximum possible value of their dice rolls to their attacks.

Consider a level 10 rogue with a Dexterity score of 20 (+5 modifier), wielding a shortsword. Assuming the rogue has sneak attack, this means a successful attack with the weapon deals 1d6 + 5 + 5d6 damage, for an average of 25 damage. 
The normal critical hit rule would mean the rogue instead deals 2d6 + 5 + 10d6 damage, an average of 47 damage, on a critical hit.
However, under the "Add Max Damage" rule, the rogue instead rolls (1d6 + 6) + 5 + (5d6 + 30) damage, an average of 61 damage. 
Notice that 6 and 30 are the maximum possible values for their matching dice rolls. 

As this rule is automated by Avrae, you do not need to handle any manual calculations of your own in combat. Just be aware that as much as this makes your characters' critical hits more lethal, it also means the critical hits of your enemies are also more lethal.