Yes she almost always somehow sneaks behind Raymesis and scares him.
It’s also funny to think Selena has a morbid way of speaking and dark sense of humor.
She’ll give a backhanded compliment to Raymesis like “With your personality your death will be quite will be quite soon yet unforgettable” It would go over his head and he thought she meant he’s unforgettable.
If Glombrox was being chased by a giant monster she would say. “Don’t worry Glombrox, with your size and smell it would only take 3 days for the beast to fully digest you” or if he got lost and the group was looking for him she would say “Considering that frogs are considered a delicacy hopefully he has not been devoured for sustenance”.
Most of the time she’s not saying it out of malice she thinks a joke would lighten the mood but it instead makes her look more creepy.
PH YEA I CAN PICTURE THAT, I can also picture her making a joke about glombrox, raymesis laughing his ass off abt it, then she immediately makes a joke about him and he takes a second to process it and is like "what the fuck did u just say to me"
Raymesis and glombrox def beat the shit out of each other when they are pissed off at each other, but if any of them tried to fight Selena she would easily be able to beat them, but I don't think she'd join in on pointless anger fueled fights she'd just causally move out of the way as, say, raymesis lunges at her, she's moved to the side quickly, then he comedically slams into a tree or something and she'd laugh about it and he'd get embarrassed and tell her to shut up and it would just make her laugh more 
OK, so you know all those princesses from Rayman Legends, including Barbara? Here's my headcanons.
Barbara and Elysia were twins and lived together with their parents for the first two years of their lives. They got separated because their father couldn't stop being a cheap-ass colonial bastard who liked making shit worse for the serfs and servants. Barbara and Elysia's mother (who was more progressive and only married their father as per an arranged marriage) was forced to only take one toddler and raised her to be a rebel fighter until her death. Barbara never knew Elysia was her sister until they met up as young adults in battle.
Aurora and Twila are three years apart and hail from a kingdom populated by bean plants. They constantly quarrel over what way is the best way to rule their kingdom, which only serves to piss off their loyal subjects. When a toad army invades their kingdom, they fight with each other over how to get rid of them. Aurora simply wants to intimidate them into leaving, while Twila wants to use fire against them. (She's a pyromaniac, OK?)
Estelia and Selena are princesses who are in charge of taking care of the souls of the dead. Estelia manages the innocent souls, while Selena takes care of the evil ones. Selena feels jealous of her twin since she is depressed from seeing so much evil in the world and eventually...disappears. Estelia was under the impression of Selena being chill with her line of work until learning about her sister running away. She constantly sends out guardians to find Selena but hasn't had any luck so far. Meanwhile, Selena unfortunately falls under the influence of Mr Dark...
Ursula and Emma are a couple of tech-savvy princesses who have to deal with an army of underwater toads that are trying to kill them. Both sisters seek a device that creates portals to different worlds, and they want to throw the toads through such a portal. (But they haven't considered the possibility of the toads becoming a danger to other people, lol) Anyways, Emma gets separated from Ursula on a mission through a labyrinth, leading to her older sister to think she died. She is working hard on defeating the toads and avenging her (not so) dead sister.
Olympia and Sibylla are two princesses who are descended from Athena, goddess of wisdom. The two of them defend Olympus from attacks by demons and still stick by each other no matter what. Sibylla is too curious for her own good and often goes monster hunting (namely the Minotaur), leading to Olympia to go out and drag her arse home before she gets killed.
So yeah, here's the backstories I made up for the main line of princesses from Rayman Legends. I know that there are MORE, but I can't be arsed to go through them. Also, in my headcanon, each set of sisters isn't related, i.e., Barbara and Elysia aren't related to A+T, E+S, etc. Asafjdhvzd