It took me three sittings to finish these 20 CGA levels, but I beat the vast majority of them in one sitting.
Some of them took 1 try, some 2, and some 5+ tries. A lot of my mistakes were stupid ones though. If you're good enough to beat the regular levels, you're good enough to beat these bonus ones as well. The same basic skills are tested across them and the challenges aren't extremely varied (though each CGA level uses concepts from the "world" that it's part of, e.g. ice, fireballs, blowing clouds, swinging spikes, etc.). It all comes down to good timing and using each of Grannie's three abilities to its fullest. I didn't notice too much of a difficulty hike; things seemed pretty even from level to level, with some exceptions of course.
Playing as Grannie turns enemies into cake walks. The previously-anger-inducing sword enemies are no match anymore.
After getting caught back up with the game's general mechanics, I was able to blow through most of the bonus content. The new levels were a lot of fun! I'm actually glad they made for a solid challenge and not an overly frustrating one.
Great job, Renegade Kid. This was a great freebie.