Infernal Quirks

Devils and demons have their own weirdnesses. Making them generic ("a marilith") is silly - these are CR (a bunch) creatures. Each ought have a story, a name, all that.

Fiendish Quirks (general)

 - Wears comically large shackles. Huge, chunky wrought-iron rings the size of barrels wrap around wrists and/or ankles. Short lengths of chain trail behind. All over the black iron is spotted with patches of red rust.

 - Has lost an arm, and it is replaced with chaositech of some kind. Bands of red gold, elaborately filagreed and hammered so so thin, form an elegant arm and hand, with petite and pointed talons.

 - Clearly some draconic was mixed into this bloodline at some point. A broad set of striped horns, full maw of bent teeth, and fine pattern of scaling make this obvious. And, of course, the breath weapon.

Demonic Quirks (chaotic)

 - A gray sludge constantly pours off this demon, leaving a slime trail behind. It smells like asphalt and bleach, and every so often an ooze bubbles up out of it if the demon stands too long in one place. (Juiblex)

 - Every step sounds like crystal windchimes. As it walks there's a pleasant tinkling. As it runs there's a frantic crashing that sets the heart to beating wildly. When it charges into combat everyone that can hear must check or panic.

 - Smells and tastes delicious, like honey and spices. Their skin has an iridescent sheen to it, and if licked the taster is thrown a real loop. That's the good drugs.

 - When slain, a chrysalis forms around the remains. The demon rises again in 1d6 days, now modified to resist whatever killed it - though these immunities are exceedingly narrow (e.g., it might be immune to "taking 12 damage from slashing" from now on). This guy, of course, gets way more powerful over time, like Doomsday.

Infernal Quirks (lawful)

 - Hideously fat, and gets around in an amusingly undersized golden throne. The throne floats, bobbing and weaving through the air unpredictably, ala Baron Harkonnen.

 - This devil keeps trophies of the contracts it's sealed. Dozens of tiny colorful lockets, each one with a curl of hair, drop of blood, or a tiny portrait, adorn the monster. They click and chime as it walks.