Also not considered here are "cameo crossovers," where characters have no interaction with a developed plot, but merely appear as "walk-ons," usually for the purpose of a quick joke.
However, the "Council of Doom" episodes are slightly more developed than the "quick joke" example I provided in my earlier essay.
The main plot of the mini-saga goes like this: six of Space Ghost's most vicious enemies team up-- becoming the "council" of the title-- and then take turns trying to destroy the spacefaring hero. The six of them, seen blow, are (going clockwise from the well-known Zorak) are Zorak, Creature King, Metallis, Spider Woman, Brak, and Moltar.
In four of the encounters, the villains zap Space Ghost into some other cosmos. The hero is then set upon by hostile forces in that universe, only to be saved by one of four heroes native to said universe: respectively Shazzan, the Herculoids, Moby Dick and the Mighty Mightor. (Note: the first two had their own shows, while the latter two shared one cartoon-berth.)
Thus, Space Ghost never interacts with any of the other heroes for more than a minute, if that. However, I find that these brief encounters-- patently intended to advertise the new cartoon-kids on the block-- are still important to the "Council of Doom" plot, at least more so than you would get with a throwaway joke. And in at least one case, there's a good "science vs. magic" vibe. In the Shazzan segment, Space Ghost's powers are useless against the sorcery of the evil "Sultan of Flame," while the heroic genie's abilities easily trump those of the mystic evildoer.
A later 1980s cartoon had Space Ghost and the Herculoids cross paths off-and-on. But as limited as these crossovers were, they captured perfectly the pure fun of the 1960s era, whereas the 1980s show seemed a pale spectre of the originals.