4* Black Bold doesn’t speak a lot or Deadpool with a sewn up mouth?
Or Silence herself (another symbiote 
)?
Fount also the silent war comics.
And there is Luna Maximoff
Mum’s the word… Queen Mum… Queen Peggy!
Mother->Mother Righteous->The Righteous Brothers->Unchained Melody->Melody Guthrie->Aero->Bubbles->Absolutely Fabulous->Fabulous Five->
Nanny, perhaps?
Halloween, joke character… The Living Mummy
The first thing that came to mind for me was Dinah Soar, but that’s mainly because I’m currently reading Vol. 1 of Thunderbolts and the GLA made an appearance there early on. Though, judging some of the most recent characters they’ve added to the game, she doesn’t seem that weird of a character to add at this point.
I can see “mum” being a double meaning for the flower, and not speaking, and end up with Man-Thing as a Halloween type character.
Or maybe Plantman….
We could use another Halloween character. I like the suggestions of both The Living Mummy and Man-Thing. Speaking of Man-Thing, Werewolf by Night in Color just released within the last week. That could be a potential tie-in (though it would be a bummer to not get Werewolf by Night directly).
I’ll add that Mum’s the Word is actually a phrase. It’s the term for a secret that is best left as a secret. So the hint may be for that instead of a literal mother.
Wasn’t there a run of Thundercats printed by marvel?
Could be wrong… But I’m guessing Mumm-Ra.
Hopefully it’ll be someone who feeds venomsaurus rex