The tears multiplier can cause Isaac's tear delay to decrease beyond the normal cap of 5.
The speed multiplier cannot cause Isaac's speed to decrease or increase past the normal range of 0.1 to 2.0.
The multiplier overrides the speed up effect of A Pony or White Pony, which normally raise Isaac's speed to 1.5 if it is below that value.
The hidden maximum speed value also gets the same multiplier, which may further cap Isaac's speed.
The multipliers are chosen in a way that keeps their total product roughly the same; the item will most often increase two and decrease two of Isaac's stats, although it can increase three and decrease one or increase one and decrease three. Larger increases are balanced by larger decreases.
Book of Virtues: Spawns a black glowing die wisp on the middle ring. Each wisp has a random damage and fire rate assigned to it. Wisp health is not randomized.
The sprite for D8 has an 8 and a 7 below it, but judging by how real D8 dies look, the 7 should be a 5 instead.