batman has a lot of grounded villains so its probably the one here where they can really keep it grounded similar to nolan
they already made penguin more human in comparison to burtons or the comics, joker and harley are obvious just psychological nemesis, scarecrow, hush, two-face, hugo strange, mad hatter, black mask, deathstroke, redhood and the court of owls are all just humans with realistic abilities/skills… even bane who you can just get roided up and expand on what nolan did (which is perfect to put alan ritchson in a mask as dude just looks bigger and towers most dudes)
nolan was able to ground Ra’s Al Ghul too just like he did bane so the only ones left thats on a more fantastical side are freeze, manbat, croc, ivy and clayface and even clayface og version isnt the one we know from the animated series
someone like batman who laughs is definitely fits in more in gunnverse but they can easily make 5-7 grounded films out of battisonverse