Casper's First Christmas was the second of two primetime specials that were part of the package when Hanna-Barbera acquired a license to use the Friendly Ghost in a futuristic Saturday morning series.
However, Casper & The Angels turned out to be a flop, and this special, like the Halloween show, outside of the series' continuity, would be Casper's coda at H-B. And, oh, did he go out with a bang!
H-B decided to test the waters and had Casper (Julie McWhirter, ex-Wacko!, The Rich Little Show) & Hairy Scarey (John Stephenson) interact with Yogi Bear, Huckleberry Hound, Snagglepuss, Augie Doggie, & Doggie Daddy (all voiced by Daws Butler, except for Doggie Daddy, as Stephenson essays a dual role, replacing Daddy's original portrayer, Doug Young), and, of course, Boo Boo (Don Messick).
As you could probably tell, even though she's an impressionist by trade, McWhirter was unable to duplicate the voice work of her predecessor, Norma McMillan, and, as a result, Casper just doesn't sound right, which would explain why his run at H-B was a disaster. The following year, Yogi & the gang would return in the syndicated TV-movie, "Yogi's First Christmas", which now can be considered a prequel to this show.