Target cycling on green?
 

So I've seen people being able to swtich between two targets without using something like "nearest target. They target 1 mob, then another. The they can instantly switch between those two previous mobs they target. I don't see any option that does this and I don't see anything on the wiki indicating the function being used here.

That's the tab key.

"Toggle last two targets"

Well for some reason my option menu is all mangled /clipped and I couldn't even see there was an an entire selection for "Targeting". After I blindly clicked around in frustration it popped up.