In short, Melly's approach to sleeping at night is extremely energetic and involves full use of all of her pointy bits. She occasionally burrows under the covers, which is pretty cute, but seems to get bored quickly, and so focuses her attention on trying to wake me up to play. (I should add that I need a minimum of eight hours of sleep. Twelve is better.) Melly has a couple of methods of waking me up: if I lay on my stomach, she bounces around on my head and shoulders (claws!) chewing my hair. If I lay on my back or side, she bites my nose and/or chin - hard. She also likes to pace back and forth across my pillow - the fact that my head is in the middle of my pillow does not deter her. Aside from the claws-on-scalp issue, I really prefer that those litter box paws not touch my pillow. Bed, fine. Pillow, not so much.
Scarlett is a quiet and injury-free snuggler, and causes minimal sleep interference. However, Melly likes to chase Scarlett off the bed as soon as she's settled in, which usually involves hissing and growling and also wakes me up.
I have tried tiring Melly out before bed with lots of vigorous playing, but that only seems to quiet her down for an hour or so, then she's back to her old tricks. The fact that she naps for much of the day, including at least a couple of hours in the evening, probably has something to do with this. I have tried just allowing Scarlett in the bedroom, but that doesn't work out well because Melly wants in and Scarlett wants out for litter box use and food and much loud meowing from both ensues.
And so, neither cat is allowed in the bedroom at night. I miss Scarlett's purring and cuddling, but I do not miss Melly's efforts to maul me. I plan to try again once she is through with her teething and calms down a bit, but until then, sleep takes precedence.
Here's a video of Melly gnawing on Scarlett's tail. Scarlett put up with it for a surprisingly long time (that's her purring in the background) before swishing her tail out of Melly's grasp and stalking away.