Each other non-Aura enchantment is a creature in addition to its other types and has base power and base toughness each equal to its converted mana cost.
10/4/2004 Does not animate itself. But can be animated by another Opalescence.
2/1/2006 With a Humility and two Opalescences on the battlefield, if Humility has the latest timestamp, then all creatures are 1/1 with no abilities. If the timestamp order is Opalescence, Humility, Opalescence, the second Opalescence is 1/1, and the Humility and first Opalescence are 4/4. If Humility has the earliest timestamp, then everything is 4/4.
8/1/2008 A noncreature permanent that turns into a creature can attack, and its abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of his or her most recent turn. It doesn’t matter how long the permanent has been a creature.
10/1/2009 This is the current interaction between Humility and Opalescence: The type-changing effect applies at layer 4, but the rest happens in the applicable layers. The rest of it will apply even if the permanent loses its ability before it’s finished applying. So if Opalescence, Humility, and Worship are on the battlefield and Opalescence entered the battlefield before Humility, the following is true: Layer 4: Humility and Worship each become creatures that are still enchantments. (Opalescence). Layer 6: Humility and Worship each lose their abilities. (Humility) Layer 7b: Humility becomes 4/4 and Worship becomes 4/4. (Opalescence). Humility becomes 1/1 and Worship becomes 1/1 (Humility). But if Humility entered the battlefield before Opalescence, the following is true: Layer 4: Humility and Worship each become creatures that are still enchantments (Opalescence). Layer 6: Humility and Worship each lose their abilities (Humility). Layer 7b: Humility becomes 1/1 and Worship becomes 1/1 (Humility). Humility becomes 4/4 and Worship becomes 4/4 (Opalescence).