Monstrum is a curious creature. Simple, however that curiosity might (or will..) become more twisted and sinister as she begins to actually prod & poke at whatever or whoever she is curious in. Imagine an apex predator studying and curiously wandering around its new environment or wherever it has never explored before. It'll become more comfortable as time goes by as it stalks whatever lives in this expanse. Until, it makes a move if its own.
Monstrum was curious on what Shepperd was, and during her "juvenile" days, Monstrum wanted to dissect everything and everyone she had faced. By any means. Those means, being actually dissecting and literally dismantling what she found interesting.
Pretty much... Like a curious and invested kid dissecting a frog during biology class.
Monstrum enjoys learning, ever since she first had dismantled her mind to escape the Null and found.... what it was like outside the abyssal void she was basically stuck inside of since her birth and devouring of Prime Nulla.
I imagine Monstrum stalking Shepperd after their first encounter with each other, managing to worming herself into Shepperd's dimension--and just curiously yet meticulously watching from afar before either she revealed herself or Shepperd had finally noticed & found her.
Lucky for Shepperd, Monstrum had matured enough to not "carelessly" dissect him like she has done to many primordials, demi-gods, gods, demons, monsters, other eldritch & cosmic horrors, humans, etc etc..
I won't lie, and admit that- Monstrum is kinda like a leopard seal?
Fierce & Intimidating: It implies you are not to be messed with. Leopard seals are powerful hunters, so someone might use this to describe a person who is sharp-tongued, highly competitive, or tough in arguments.
Independent & Solitary: These seals typically live and hunt alone rather than in large groups. The label can refer to a "lone wolf" type who prefers doing things on their own.
Curious but Bold: While they have a terrifying reputation, leopard seals are also known for being highly intelligent, curious, and playful when interacting with divers. It could mean you are bold, inquisitive, and have a complex personality.
Protective: In some wildlife stories, these seals have shown surprising protective behaviors, suggesting the person might fiercely guard their friends or loved ones.
P.S Leopard Seals and Monstrum are eerily close in symbolisms and behaviors (??) Shepperd gifting Monstrum a Leopard Deal plushie be like /silly
Shepperd playing in Evigheden with his little creations, not noticing the overbearing being of doom in the corner/silly:
Shepperd's brother might have noticed a smidge, only due to pure feeling + intense premonition, though I don't think he'd know how to place it.
I do think that maybe the Shepperd sewed her the plushie with Evighedian string, making the gift practically unbreakable as well.
I like to think that sometimes the Shepperd used to appear near Monstrum and give her Seal plushies with a bow with butterflies on it. The butterflies being a courtesy of his brother.