Adding Pathfinder style demoralize to 5e

[Herr Doktor]

Like the thread title says: I've been thinking of adding the demoralize opponent option for Intimidate (-2 to hit hit and saves) to my 5e games.

Would appreciate any feedback (good or bad) from anyone who might have tried something similar.

Would also appreciate any advice on setting DCs: I'm thinking, given a Medium-size character, 15 for Small or Medium opponents, 20 for Large, 25 for Huge, and 30 for Gargantuan.

[Arkhios]

-1d4 (-2 on average) to relevant rolls would be in line with similar 5e effects, since flat bonuses and especially penalties are rare.

I'd make it an Action and only affect one creature, because the effect is basically same as Bane (1st level spell), which affects multiple targets. In general you shouldn't make an "at will" and readily available ability stronger than a spell of 1st level or higher (being equal to a cantrip is more balanced).

As for the DC, I'd either make it a contested skill check (your intimidate vs target's insight), or wisdom save against DC = 8 + your proficiency + your charisma.

5e doesn't do size penalties, so I'd refrain from implementing it myself in terms of different DC depending on size.