Level
1st
Casting Time
1 Action
Range/Area
30 ft
Components
V, S, M *
Duration
Concentration
1 Minute
School
Enchantment
Attack/Save
CHA Save
Damage/Effect
Debuff
Up to three creatures of your choice that you can see within range must each make a Charisma saving throw. Whenever a target that fails this save makes an attack roll or a saving throw before the spell ends, the target must subtract 1d4 from the attack roll or save.
Using a Higher-Level Spell Slot. You can target one additional creature for each spell slot level above 1.
* - (a drop of blood)
I have no idea why an Oath of Vengeance Paladin would ever burn an action to cast this.
Not everything is about how a given spell interacts with your own class features. Sometimes it's about allowing allies to more consistently counterspell, banish, polymorph etc various important targets. Few things have high cha saves.
does this only affect the first attack/save the creature has to roll, or all of them for the duration?
All of them, for the duration.