I like to keep a number of pre-rolled d20 results on a table/list in my DM notes for a session. This table is used when I want to either roll away from the players or just to speed up the game.
A perfect example for this is if a creature (say a goblin) wants to sneak away from the party. I may use the table of prerolled results instead of rolling in front of the party because I may not want to notify them outside of the game (avoiding metagaming here) that something is up. Sometimess, it might be perfectly fine to roll and watch fear set into the players' faces.
A few options..
- Pre rolling
- Rolling when it happens
- Asking a random player to roll a d20 on your behalf for no reason