D20

The D20 is the icosahedron everyone pictures when tabletop RPGs come up — twenty triangular faces, numbered 1 through 20, rolled to see whether an action succeeds. It’s shown up on t-shirts and jewelry far beyond the hobby at this point, but its actual job is simple: add your modifiers to the roll and compare it to a target number.

It’s also the die behind the hobby’s favorite drama — rolling a natural 20 or a natural 1 is what people mean by a critical hit or critical fail, and those two extremes get remembered long after the rest of the session. If a game on the shelf lists a D20 as its main die, expect a night built around that kind of tension.