The New Mutants was by no means a disaster, but watching the movie, it was easy enough to see why Fox wanted to move forward with reshoots. Those were scrapped when Disney acquired the studio, of course, and Josh Boone's original cut ended up being the first major blockbuster in theaters when they re-opened over the summer (beating Tenet to the punch).
Demon Bear was the lead villain in the Marvel Comics adaptation, and a formidable adversary for the mutants who found themselves at the mercy of Dr. Cecila Reyes.
Now, concept artist Deryl Braun has shared some of his early designs for Demon Bear, one of which bears a striking resemblance to the Venom symbiote. That was no doubt coincidental, and there's a vast array of alternate takes on the classic comic book villain to be found here.
It's hard to imagine when the New Mutants and Demon Bear will return to the big screen, though Marvel Studios will almost certainly make use of some of the characters in the coming years (fans would definitely like to see more of Anya Taylor-Joy's version of Magik, anyway).
Check out this concept art from The New Mutants below: