Filmation had thought they could make hay by acquring a license to bring Mighty Mouse & Heckle & Jeckle back to television in 1979. Unfortunately, it didn't work out quite so well, largely because the original shorts with these characters were readily available in syndication. A rare Filmation original, Quackula, was H & J's backup feature (with Frank Welker voicing Quackula, Heckle, & Jeckle), but good luck finding any of his shorts in English these days.
Quackula shorts are hard to find----in English, but one wonders if he was the inspiration for the British Count Duckula a few years later. As for Heckle & Jeckle, what few shorts had been available have been removed from public consumption. All that is left is this promo, shown in the summer of '79, and narrated by then-staff announcer Danny Dark (Super Friends), who must've found it amusing that this would air opposite his ABC series.