the Grid Alien was born from Rosseaubecause it just makes the most sense to me.
The Rookie from the 2010 game was a cyborgThat's why he can block what should be lethal strikes and knock down Aliens and Predators, catch facehuggers mid-leap and walk off acid burns and bullet wounds as if they were nothing with just a stim. At the very least his arms and torso area have been reinforced. This might also be why he can't jump well or sprint for more than a couple seconds, his body's too heavy now.
Righting together? That's how Predators court each other
- Normally Predators seem to fight one-on-one against their enemies - or they set traps as assassins. One for the Scar/Lex fans - Lex thought she was fighting beside Scar as an ally, but in the Predator warrior culture a show of partnership and strength is how courting - or at least flirting - goes between males and females. Scar was young enough and impressed enough that he decided to return it.
The Elder was Scar's father
- Scar obviously came there with his homies for his ritual - he was the son of the clan leader, but he needed to prove himself just as much as any other warrior.
Scar and his hunting buddies were too young for the ritual.
- As guessed above, Scar was the Elders son, he was due to take the proving ritual soon, but not yet, so Scar and his buddies were sent to a "defunct" proving ground, by the Elder, to "train" for the actual proving, they expected it would not be a challenging hunt, being that the proving ground was out in the middle of Antarctica, so there would be little "hard meat" to hunt, being essentially a "pre-game" getting ready for a real Xenomorph hunt, Chopper and Celtic were Scars friends as well as hunting buddies, so he chose them despite them being younger still than Scar. It explains why they are so "stupid" in comparison to most Predators we see, falling for obvious traps and the like, only Scar was actually close to fully trained to hunt Xenomorphs, the other two weren't, seeing as Scars only real failing in the movie is to be facehugged, note he seems to usually try and take the long range approach to Xenomorphs, while Chopper and Celtic just jump in.
The Spear Elder gave Lex was "the Prize"
- It is similar to the usual Predator spear but more ornate, if any of the Predators had survived they would have been presented with the Spear, if more than one had survived it would have been the one who scored the most kills, Lex got it because not only did she survive, she killed a Queen which is especially difficult to do, which gave her more higher regard by the Elder.