Overall Rating: Orange. This means that
Power Word Pain is an OK spell.
Overall Notes: As long as the target has less than 100hp, they don't get to make a save to resist the effect. This makes it a decent choice when targeting a creature with Legendary Resistance. The debuff is quite potent, it provides disadvantage on attacks, ability checks, and saving throws, and casting spells becomes more difficult. Unfortunately, the effect can be ended with a successful CON saving throw so there's a good chance the effect only lasts one round. For a 7th-level spell, this is rarely worth it.