1. A
tetrahedral dice. Has four sides, hence the name "D4." Used for Wizard spells and small weapons. Also used for low-caliber firearms in d20 Modern.
2. Improvised caltrops that hurt way
more than a
LEGO brick. Incidentally, D4s are also used to roll for caltrop damage.
1. Roll 1d4 damage.
2. "Whilst the d4 isn't as sharp as a d8, it has one major bit of natural defense -
no matter what way it lands, it will have a point face-up. Because it's
the smallest die, care needs to be used - if one escapes its dice-box and
into the wild, it will wait, with its natural weapon ready, for the exact moment someone walks into its vicinity barefoot to strike, whereupon it will inflict some surprisingly-vicious puncture wounds." - "Dice," 1d4chan.