I'm near the Missouri/Arkansas border, for what it's worth.
Both L sounds involve raising the tongue, but with the light L the tip of tongue approaches the alveolar ridge (the part of your gum just behind your top row of teeth), while with the dark L the tip of the tongue does the same thing, but the back of the tongue simultaneously rises towards the soft palate (this is called "velarization", and it's the same gesture that accompanies lip-rounding to form a W sound). There may be further differences depending on accent, e.g. in Cockney accents the tongue-tip gesture of dark L is lost completely so that dark L becomes a fully-fledged vowel, and it might even acquire lip-rounding and merge with W. Other accents have lost the distinction as well and generalized either light L or dark L to all positions (e.g. Scottish English tends to use dark L everywhere).
In the older pronunciation of "falcon", there's no L there at all, light or dark. It was borrowed from Old French "faucon", and the L was restored in spelling via Latin influence in more or less exactly the same way as the B in "debt".
Hell, I'm pretty sure captain falcon in smash brothers also has a hard L in "falcon punch!"
It's "Karen" in normal conversation, but if she brought storebought cookies to the potluck it's "Kar-in-nuh", with the emphasis on the last syllanble.
In my head, these are called "spite syllables" :)
That would usually be coupled with a very veiled reference to how she put in the minimum possible effort while indirectly insulting her entire bloodline: "Oh, don't you just feel for Karen? I don't know how she gets anything done with those kids of hers."
Alternatively, if the speaker wants to embarrass her in front of someone with a higher social standing; "Karen, these cookies are just the best thing ever! What do you put in these to make them so good?"
Hah. Where I live this would mean they have marijuana in them.
I'm unsure of the difference between the old and new here. Does anyone pronounce the "l" in "falcon" by touching their tongue to the roof of their mouth?
I pronounce the "l" similarly in "fault", which is kind of "fau-t".
(If you're just referring to the "a" sound, like the a in "fall" vs "fat" then that's a different question, but I think quite regional.)