As for the reason Gargotec does not sound like Gargamel in "Mummy Dearest," it was reported that Paul Winchell (who voiced Gargamel) had walked off the show when he read the scripts for the Season 9 episodes.
"Hogapatra's Beauty Sleep" is the only time in Season 9 that depicts Hogatha's doppelgänger.
"Mummy Dearest" is the only time in Season 9 to depict Scrupple's doppelgänger.