For pretty much anything that is magical, (and not Directed Spells), we use a BAR and the Basic Spell Attack Table, and the Resistance Roll Table, along with Racial/StatItem RR bonuses.
Importantly, we feel there is a bias in the game towards PCs who typically get both BAR bonuses (especially at higher level) and RR bonuses from stats and (again at higher level) from items. Whereas NPCs and monsters often get no BAR or RR modifiers. So, as a blunt rule, where not otherwise specified, I give NPCs/Monsters a bonus to both their BAR AND RR mods equal to MAX(10, 2xLevel). Otherwise, especially as the level of play increases, the likelihood of PCs landing magical effects on NPCs begins to far outweigh the other way round.