Well, that makes this easier
Damnbeast
Imagine a tiger. Now, make it at minimum 3-5 meters in length, weighing in at roughly two to fever tons depending on size, and make it the most angry monster you have ever met. Give it six legs, each with a gecko pad like foot with claws that can shred tank armor, skin that laughs at anything hand held. It's mouth can expand to swallow humans while, and the damn thing is terrifyingly smart. It learns. You can only set a trap for it once, and if it lives that trap never works again, and it's smarter the longer it lives. It is a thing of horror, and the Only reason it's not killing everything is because it's a genuine solitary apex predator. It's territory seems to be massive, spanning hundreds of miles that it claims against all competitors. And finally, as if that wasn't bad enough, the damn thing can apparently use biotics. Like, actual semi coherent biotics, not just a natural trait. It can make itself lighter or heavier, it can move like greased lightning, and the older ones can generate there own damned biotic barriers.
This thing is an Apex Monster. Fear it.
Stalker Gheists
Stalkers are gods way of letting the people of Perkuwonos know he hates them. These little bastards are the definition of horrifying. For one, they can turn near invisible, leaving only a shimmer in the air to Mark there location. For another, the damn things have Hands. And are smart enough to use them. They can open doors and windows, operate locks, press buttons... you name it, these creepy little monsters can fuck with it. And they can generate a static charge for self defense, enough to act like a taser on people it hits. They also have the horrifying ability to mimic sounds. Perfectly. Like someone calling out to someone else on the perimeter, and when they go to investigate they find no one there, until the beast drops down and shreds them. The only saving grace is that the monsters are small, barely more than child sized, and unable to pierce modern armor. Unfortunately, they can figure out guns, but no ones dumb enough to leave armories unguarded like that on this hellhole of a planet.
Doom Turtle
These guys are actually some of the easiest beasts to deal with. Mostly, because the creature in question appears to be a scavenger more than a hunter. It forms a large biotic barrier around itself, and whenever anything hits the barrier it hits back with a contact warp. It shreds anything that touches its barrier, then floats over it and eats it. The barriers are pretty tough, but all that's really needed to drive them off is a decent lightning strike. Or a machine created fake lightning strike.
So. Thoughts?