The spell Bane can be incredibly useful in helping the whole party. It allows the caster to impose a CHA save on 3 creatures (more at higher levels). If they fail, then they subtract a d4 for every attack or save they make.
This spell is most useful against non spell caster combatants (ranged or melee). For spell casters, it will be less effective since many spells require a saving throw, not an attack roll.