Each type of idol has a weight which determines its chance. The chance for each type of idol is
weight / sum of weights.
Only the first item generated when an enemy dies has a chance to be an idol, so quantity and quality stats don't affect idol rates. Before level 5, enemies don't drop idols. From level 5 to 13, the idol chance slowly increases, and at level 14+, idols have a 3.5% base chance to drop. If there is a level difference of 5 or more between the player and the enemy, the chance is greatly reduced (base chance is divided by
(Level Difference - 3)^2).
(at level 20)
(at equal levels)