1 pip - Seems to reroll all the upgrades on the player, but without the other effects of the "6" dice room (see below).
2 pips - Rerolls the pickups in the Room like the D20.
3 pips - Rerolls the pickups in the Floor like the D20.
4 pips - Rerolls any items that have appeared on the floor but weren't previously grabbed like D6.
5 pips - Rerolls the current floor, similar to the effect of Forget Me Now.
6 pips -Seems to reroll all the upgrades present on the player at once. This does not seem to affect trinkets, pills or cards, but can change an activated item into a passive one and possibly visa-versa. Also randomizes all items on the current floor like D20.
The dice rooms are still not well understood, and sometimes have different effects than described above.
The room must be unlocked with two keys.