hi all,

i really can't understand the different between Passive effect and Constant effect.

Casterly Rock

Text:
Lannisport, Stronghold Immune to events. During the challenges phase, your unique characters gain stealth

is this card's ability Passive ability or Constant ability?

and here is the question i met yesterday

when challenges Phase i use Meera Reed blank Casterly Rock,my opponent said this is Passive Ability,so when challenges Phase started the unique characters gain stealth no matter what condition to this location because FAQ said:

(3.11) Definition of Variables
Constant Abilities will constantly check and
(if necessary) update the definition or count of
their variables.
Triggered Effects and Passive Abilities define
or count their variables once (when the effect
is initiated), and the variable is then constant
throughout the duration of the effect.
When an effect checks a variable but there is
no number present or has no quality capable
of being checked (STR, power, cost, etc.) the
variable is counted as 0.

Casterly Rock's ability is a constant effect with a condition, like Murenmure's gaining of his response during Marshalling.

The primary difference is that a passive effect has a point of initiation that can be interrupted and canceled. A continuous effect does not. So, for example:

1. "If X is true, Y is also true" would be considered continuous.
2. "If X is true, Y happens" would be passive.

#1 is Casterly Rock. It is tempting to think that Casterly Rock is actually #2, but the other thing to recognize about passive effects is that they initiate and resolve immediately. For a passive effect to apply beyond that resolution, there has to be a stated duration for it. So, for Casterly Rock to be passive instead of continuous, it would need to be in the format "If X is true, Y happens until Z. "

Without that duration, you're back to #1 as the correct interpretation for Casterly Rock.