Goodness me, I don't have any tips because I think they look just great. Maybe a liiiiiiiiiiiiiitle swelling on one of the ankles but I wouldn't have thought that at ALL if you hadn't fed me the idea , I really think they look great the way they are...plus you said they're for a monster anyway? Love the way you even got knuckles and indentations for finger/toenails.
As for the exacto knife sticking, did you grease it w/crisco?? Just a thought, I have no idea if that would help lol.
I looked at your cakes and your fondant charaters are so good! You have the porportions done well. I have the most difficulty keeping the porportions for the parts correct so they look right!
LOL I also realize now that I misunderstood your title, when you said "monster webbed feet" I thought you meant they were for some sort of monster character; now I realize that you just meant you thought they were monstrous!! ROTFL, DUHHH!!
Anyway I stand by my original assessment, I think they look fine. If you think they look "webbed" because the knife didn't cut all the way thru/or the digits stick back together after being cut, I really disagree, I think they just look "characterized" which is how they are supposed to look! If you don't like the look you can prob. use your x-knife to nudge them apart a little more and then...maybe dust w/cornstarch so they stay separate while they dry? Seriously, though, I think that's nit-picky, they look good!!
I think they're great. You've got perfect details, a great skin tone...I'd be delighted to have created those feet and hands
Maybe dipping the exacto knife in a little cornstarch would help it keep from sticking.