Predator isn't the only franchise that's enjoyed a surge in popularity; the Aliens xenomorph's first appearance is climbing, and now would be a good time to invest. 

Yesterday, I brought you up to speed on the Predator's first appearance and how it's quietly gaining value. Today, let's check on a few other Predator keys and its eternal nemesis, the xenomorph.

You can't talk about the Predator without mentioning Aliens. Although these two franchises were created 10 years apart (Alien terrorized Sigourney Weaver in 1977; Predator cut off Carl Weathers' arm and chased Arnold Schwarzenegger through the jungle in 1987), thanks to Dark Horse Comics, the two franchises essentially merged throughout the 1990s and 2000s.

These days, the Marvel Cinematic Universe has set a new standard when it comes to characters in separate film series sharing a universe. Some might believe the modern shared cinematic universe began when Tony Stark found Thunderbolt Ross in a bar at the end of 2008's The Incredible Hulk. (I realize that Nick Fury appeared in the Iron Man post-credits scene two months prior, but he hadn't been established in another film before then.) However, Predator and Aliens crossed over in 1990 with Predator 2. As the final act of that movie was wrapping up, and Danny Glover found himself surrounded by elder Predators onboard their ship, sci-fi nerds like myself lost their minds when a xenomorph skull hung in their trophy case. While it took 14 years for the two to officially meet in the cinematic universe (and, boy, were we disappointed), Dark Horse brought the two together in 1990's Dark Horse Presents #36.

DHP #36 isn't jumping as much as Predator #1, but there's still noticeable movement. Within two years, a 9.6 has risen from $49 in 2016 to $123 this past May. Even a 9.0 is on the move. Last year, one sold for $16, but again in May, one sold for $33. It will be interesting to see where this ends up by the end of year.

Two years before DHP #36, there was Aliens #1, and it is worth paying attention to. Like Predator, the Aliens franchise was resurrected after the simply horrid AVP films. Personally, I thought AVP had destroyed the Aliens franchise by ruining the timeline and making a mockery of the original films. However, the xenomorphs have returned to movie screens with Prometheus and Alien: Covenant, which have put the series back in the spotlight. Investors will want to watch Aliens #1, as it has been climbing this year. A 9.8 is only $15 short of the record high sale after a $775 sale on August 8.

The Aliens #1 grade that's really on the move is the 9.6. The past two sales have been record-setters at $180 and $200. Before those two, the most a 9.6 had brought was $153 in 2013. Since then, it didn't surpass $145 until this past May. Anything lower than this isn't fetching big returns, so if you're going to scour eBay for one, stay with the near-mint grades.

I can't talk about Predator keys without mentioning my personal favorite crossover, Batman Versus Predator from 1991. As far as investing, there's not much to talk about. It's not worth much, and I don't expect it to make any significant gains anytime soon, but it is simply a great series that I highly recommend.