What is Twenty Twelve?

Twenty Twelve is a roleplaying game system that uses the 1d20 and 1d12 dice for all of the game mechanics.

Why use the 20 12 system?

Using the 1d20 and 1d12 allows the player to easily remember what dice to roll for every action.

Besides that, the d20 and d12 roll very well and can produce a wide variety of outcomes.  Using this simplified system allows the game to move quickly without constantly having to look up what dice to use.