Actually, I've just looked it up. Hasbro *didn't* ® "Enchantress", and the Thor/Enchantress Secret Wars pack lists Amora as "Marvel's Enchantress".
And the only live ® for "The Enchantress" in a toy-related field (albeit not quite the same category MotUC figures are listed in)? This one.
Given Filmation rights, they might just be able to do this...
As soon as an ® is granted, that's it, same as "Megatron", "Optimus Prime", "Skeletor", etc. Mattel/Hasbro/whoever could apply to have it struck down as untrademarkable due to it being a common word, sure - but they wouldn't, since that would lead to tít-for-tat. (i.e., If Mattel got a Hasbro ® for something like "Enchantress" struck down, how vulnerable would Mattel's ®s like "Sorceress", "Man-at-Arms", "Bow", "Buzz-Off" and even "He-Man" be to ALSO being struck down for the same reason?)