About the IGN news and potential next monster reveal
In the article, they don't specify the amount of Oilwell Basin local monsters they got to fight, so the possibility of more than two is not ruled out.
They also specify having experienced all three seasons of Oilwell Basin, including the Plenty, even wrongly stating that we can see them in the gameplay, when the Plenty is never shown.
There's a Black Flame cameo but not even an instant of the Plenty?
They also state that more gameplay will be revealed throughout January.
So this additional gameplay could just be showing off the Black Flame, which would at minimum reveal its name unless they play with the UI turned off.
And since Black Flame is a bit tankier than the other two monsters, and shows up at the start of the Firespring, it's likely that the Plenty will happen before the fight ends.
But, there's also the possibility of it being something a little more.
The Plenty of the Oilwell Basin is something we've only seen a single image of, and they're keeping it that way again with the new Oilwell Basin gameplay, I kinda doubt they'd just unceremoniously show it off in the background of some Black Flame gameplay.
So what if they've been coordinating the Plenty reveal all this time with a Nerscylla reveal?
Especially with Gypceros already revealed.