In the "My Friend Marsupilami" episode Marsupilami Gaurdians, the poison stone (also called the "skystone") is a blue meteorite that struck Polombia when the Incoaztecs were only beginning to exist as a civilization under the guidance of the first known marsupilami. The species was seen as the most powerful force on earth, until the heavens proved the Incoaztecs wrong by dropping the poison stone in the middle of the ancient jungles, and along with distroying much of the trees, it radiated the power to drain the marsupilami of its unique abillities, and almost took its lifeforce as well. Luckily, the Incoaztec chief saw the situation and, while the tribe nursed the creature back to health (guided by visions, no doubt), he and his warriors had sealed the poison stone and its distruction in the most heavily gaurded sanctum of the Marsupilquatl Temple forever... or so it seemed.
Centuries past since, and though the jungle and its long-tailed protector thrived to a new generation, Bring M. Backalive knew the legend of the one force that can weaken the marsupilami enough for him to catch it, though was too greedy to pay attention to the "almost killed it" part, thus with only a scrap of his clothing in the boobytraps as evidence, he stole the poison Stone to achieve his unjust glory, first he snuck peices of the stone into the eyes of the two toy robots Leo Dujardin (their human friend) won in a contest, knowing the marsu triplets would take one home with them overnight... luckily, it was only a small test doce to see if the legends are true, as Backalive knew that if the human family the marsus befriended figured it out and took back the big rock to be sealed back into the temple, he managed to keep enough pebbles of it to grined into fishfood so the condition of the Marsupilami family would return after recovery, tenfold, when they eat the pirahnas!
Just as Backalive assumed he has won, the animals of the jungle, greatful for all the times the marsupilamis helped them, fought back to help them, and Mars, even with deminished strength, was atleast an equal match for the poacher (though his inablillity to use his once-powerful tail was momentarily used against him).
No sooner was it that Leo's mother, Amanda, involved that Backalive desided he had enough and ran away, for now, and just in time, as this generations chief, had managed to find the rarest treebark, mushroom, and flower in the jungle which, grided together and mixed with fruit-juice, creates the antidote needed to give back the strength of the Marsupilamis.