You could throw pretty much any bad guy into the mix (from the Power Rangers franchise or otherwise), and it would work.
So it is pretty clear that there’s no one-size-fits-all answer when it comes to Power Ranger villains.
Dacre Montgomery’s comments about the team facing off against a dragon also seem particularly important, because the Green Ranger uses a dragon-inspired Megazord against the Rangers.
Some of the answers make perfect sense (such as the Rangers fighting Whiplash from Iron Man 2) while others are utterly insane.