Just to be clear (and so I don't forget this)...
Exposing enemy type (race) modifiers implies enemy defense = 0 and a 4x damage multiplier.
Exposing enemy elemental weakness via physical attacks implies attack power boost of 2x or 4x multiplier if Weak+ attribute is in use.
Exposing enemy elemental resistance/absorb via physical attacks implies attack power reduction of 2x is in play.
Exposing enemy elemental immunity (Darkness only though and only physical attacks) implies attack power = 0 (except in the case of the SNES version, it is probably 1 since more than 1 damage can be dealt on occasion).
Exposing enemy elemental weakness via magical attacks implies enemy magic defense = 0 and a 2x or 4x multiplier if Weak+ attribute is in use.
Exposing enemy elemental absorb via magical attacks (only) implies inverted damage and technically it is applied against the enemy's magic defense.
It is unknown what elemental immunity does against magical attacks though (it needs testing).
