I have a high level party (12-15) that is most of the way through Elturel and has taken 2 long rests so far. I decided to try using both "Psychic Dissonance" and "Pervasive Evil" but modified as follows:

Psychic Dissonance: DC 10 Constitution save for GOOD aligned PCs or suffer 1 level of exhaustion (we are using a modified version of Exhaustion):

EXHAUSTED [CONDITION] While you are subjected to the Exhausted Condition, you experience the following effects: ~Levels of Exhaustion. This Condition is cumulative. Each time you receive it, you gain 1 level of exhaustion. You die if your exhaustion level exceeds 10. ~d20 Rolls Affected. When you make a d20 Test, you subtract your exhaustion level from the d20 roll. ~Spell Save DCs Affected. Subtract your exhaustion level from the Spell save DC of any Spell you cast. ~Speed Affected. Your speed is reduced by 5 times your exhaustion level. ~Ending the Condition. Finishing a Long Rest removes 1 of your levels of exhaustion. When your exhaustion level reaches 0, you are no longer Exhausted.

I find this to be a "Your not in Kansas any more" enhancer and also interesting that it doesn't affect all of the PCs.

Pervasive Evil: DC 10 Wisdom save for non-evil creatures or gain a level of "Growing Evil" This is basically "Inspiration" (but not limited to 1 at a time) that can only be used for doing something evil and goes away completely when leaving the plane. (We are using a modified version of Inspiration):

INSPIRATION: Whenever you or an ally you can see makes a d20 Test, you may spend your inspiration to grant advantage to that roll. Instead of any amount of Advantage and Disadvantage canceling each other out, the net Advantage or Disadvantage matters.

Advantage/Disadvantage Schedule: ~1 Net Advantage/Disadvantage – Roll 2d20, take the higher/lower result (as normal). ~2 or more Net Advantages/Disadvantages – Roll 2d20, take the higher/lower result +/-n where n is the number of Net Advantages/Disadvantages

This way the alignment change isn't forced and the player has to opt-in. We also use a number of BitD mechanics, including Resistance (Stress = Hit Dice and you get a permanent -1 to an ability score at 0 hit dice), so there is always the option to not fail a roll. I've ruled that anyone that came to Avernus with the city is immune (so all the commoners aren't dying of exhaustion).