The d20 results that earn an Opportunity. It begins and ends at 20 by default, so a natural 20 grants one regardless of the total after modifiers. An effect that expands it lowers the beginning — expanding by 2 makes the range 18 through 20.

Summary

The d20 results that earn an Opportunity. It begins and ends at 20 by default, so a natural 20 grants one regardless of the total after modifiers. An effect that expands it lowers the beginning — expanding by 2 makes the range 18 through 20.