Several scenes establish the similarities between Godzilla and Kong: both are introduced with them killing a hostile monster and covering themselves in Alien Blood, both fight serpentine titans that they kill by dismemberment, both are shown taking an extended nap while recovering from post-battle injuries, both seek refuge in man-made structures (Kong at the Monarch outpost and Godzilla at the Colosseum) and both gain a respective power-up at the climax of the film.
Why is Kong so forgiving with Suko despite the fact that he tried to get Kong killed multiple times? Because Kong most likely remembers being similar to Suko at a young age.
It also explains why Kong doesn't have a problem using Suko as his own Titan club on the other Great Apes. Since Suko is around the same height as Kong when he was a teenager he's rightfully assuming that Suko is just as durable as Kong was around that age and size and figures Suko can take a somewhat decent amount of punishment.
Doug's Ugly Cute pudgy appearance quickly endeared him to fans, and now we know why he looks the way he does: he prefers to mooch off other Titans' food instead of catching his own! Usually, anyway.
The reveal that Skar King and his tribe of Titanus Kong's had tried to take over the Hollow Earth and surface millennia ago and Godzilla thwarted it also now gives a lot more context for why Godzilla was so hostile to Kong in Godzilla vs. Kong. He knows from experience that members of Kong's kind can be trouble and Kong leaving Skull Island along with the threat of MechaGodzilla probably had him thinking he was now dealing with two potential threats to the world's balance. It was only until Kong saves him that Godzilla realized that at the very least Kong is not a brutal dictator like Skar King who wants to conquer everything before him. In fact, when Kong took out the axe for the first time, Godzilla probably initially thought that the seal on the Skar King's prison is broken while Kong is his vanguard. Suddenly, his (misplaced) anger makes a lot more sense.
Skar King's status as a dictator over the Great Apes also explains why Kong's tribe ended up on Skull Island. It's very likely that they were one of the groups who did not want the war and instead of fighting decided to escape from Skar Kings reign. It's a powerful “comes full circle” moment in a way as the last surviving descendant of the Skull Island Titanus Kong tribe returns to essentially the motherland for him to free his remaining family.
Skar King's slaves have white tattoos/body paint over their bodies as opposed to his enforcers' red marks. It's likely they were once an entirely separate tribe that were captured and enslaved, and probably may have explained the empty palace in Godzilla vs. Kong.
Shimo's ice powers likely explains how Ghidorah was imprisoned in Antartica. Shimo, or one of her kind, probably helped Godzilla fight Ghidorah back then, which is confirmed in the novelization.
This is also the reason why Godzilla went for Tiamat aside from the energy boost. He was most likely on the receiving end of Shimo's ice blasts when the Skar King took control of her in the first war and needed the power to withstand the frostbite. The fact that Tiamat's lair happened to be in Arctic isn't a coincidence.
Despite the Titans going into hiding prior to the previous film, they seem back in full force in this one and Trapper apparently has enough "clients" to have "Titan Vet" as his profession. Given the Expanded Universe materials show Godzilla sent the other Titans into hiding due to sensing Ghidorah was somehow still alive, it makes sense they'd be back after MechaGodzilla was destroyed.
By the end of the film, Godzilla and Kong have established their "new empires": Godzilla ruling Earth on the surface and (King) Kong establishing his domain within Hollow Earth.
Considering Earth is after-all 71% ocean, the amphibious Godzilla has no problem establishing his dominance.
From what can be observed, Hollow Earth's ecosystem consist of mainly land masses with plenty of small-to-moderate sized bodies of water but no true oceans. In additions, its terrain consists of many mountains and high ridges, which Kong is far more physically capable of scaling and trans-versing.
Even though they're of similar sizes, Kong seems to have little to no problem taking care of Skar King's goons. This makes sense because Skar King's tyrannical rule over the giant apes would mean he'd get rid of anyone who could be strong enough to challenge him (which is supported by a bunch of spikes with apes' heads mounted on them in his lair) while keeping the rest of the apes who are much weaker in line. Kong, while quite young by giant ape standards, is a hardened veteran who has been fighting tough battles all his life from Skull Island (killing the head Skullcrawler at his species equivalent of 14 years old) to Hollow Earth and even survived a fight with Godzilla and MechaGodzilla themselves. No wonder why Kong seems to treat Skar King's goons as mere annoyances at best and doesn't even get mad when Suko tried to kill him twice; he'd already survived much worse odds than these guys.
Its also likely that they haven't had to actually fight someone in a long time since the war with Godzilla. From how they attempted to do in Kong it's likely that their go to method has been simply using the element of surprise to incapacitate/kill their target. One Kong proved able to fight them off despite that it all went downhill from there.
A Fridge throughline from KOTM through GvK to here. In KOTM, the tease for Gozilla vs. Kong was "What is a king to a god?" Under the doctrine of Divine Right, a king is ordained by God to rule over his people and territory. In Godzilla x Kong, Godzilla and Kong have agreed to stay out of each others' way, Godzilla ruling the surface and Kong the Hollow Earth. What is a king to a god? The one the God(zilla) has granted a domain to. In this context, Kong going to Godzilla for help against the Skar King could be seen as seeking divine intervention to enforce Kong's Divine Right to rule Hollow Earth. Perhaps it makes a lot more sense why Mothra, an actual goddess, also intervenes.
Monarch has created their version of the Hollow Earth Areal Vehicle created by Apex. Although they still call it a HEAV the design is completely different and has a camouflage system to keep it hidden from flying predator species or to blend in with them. This makes sense considering that Ilene and Jia were witnesses to the destruction of the previous HEAV by a Warbat during their first expedition to Hollow Earth.
Godzilla diving off Gibraltar looks cool, until you remember in 2014 how he sometimes causes localized tsunamis by just rising out of the sea. Depending on various factors, nearby coastlines could well have suffered substantial damage from this.
Scylla was mentioned in the credits of KOTM as having passive beneficial effects to the environment, and now she's gone kaput...let's just hope there are others of her species to take her place.
In Skar King's palace there are several cowering female apes cradling orange-furred children. It's at least somewhat implied that these are unwilling sex slaves being forced to bear his children.
Skar King is finally killed after being frozen and shattered to pieces and pounded further into shrapnel by Kong. One can only imagine the ensuing Ludicrous Gibs when the ice thaws out...
Let's hope that nobody is that stupid to try to make another cyborg out of the Skar King like those schmucks did with King Ghidorah.
It's implied Suko is Skar King's son, and of the implied children of Skar King, Suko seems to be the oldest. Given Skar King's been sealed away for thousands if no millions of years, what happened to all his older children?
Perhaps some of them are his minions? That one ape that got punched by Kong looked like it had an orange tint on its fur but that could just be the lava in the area.
Kong crosses a giant skeleton as a bridge while traversing the Hollow Earth. Said skeleton is so huge that one vertebra is almost as big as Kong himself, and remember that Kong is at least 300 feet (91,44 meters) tall. Just how big can Hollow Earth creatures get?
Shimo, an ice titan, is kept prisoner in the Skar King's palace. More specifically, she's trapped behind a red-hot river of lava. We can see clouds of steam surrounding her body, much more so than when she is in the upper layers of Hollow Earth or on the surface. This suggests that her prison is extremely uncomfortable if not outright painful for her, and given the Skar King's sadism it may even be an intentional act of cruelty to imprison her somewhere she'll be miserable.
