In Netflix's Masters of the Universe: Revelation, He-Man has suffered some of his most jaw-dropping defeats in the history of the Masters of the Universe franchise. However, He-Man and his alter-ego, Prince Adam, have suffered worst defeats in the past. And one of his most brutal takedowns came at the hand of another '80s pop culture icon, the villainous Mumm-Ra of the ThunderCats.

Despite the family-friendly histories of the franchises involved, 2016's He-Man/Thundercats by Lloyd Goldfine, Rob David and Freddie Williams II stands in stark contrast to the brightly colored cartoons it reimagines. Things began on Third Earth, where the evil Mumm-Ra had once again failed to defeat the Thundercats. Unwilling to entertain their undying servant any longer, the Spirits took it upon themselves to plan his next scheme, and after searching the cosmos and worlds beyond for a power capable of matching Lion-O's own, they discovered the Sword of Power. Rather than send Mumm-Ra to Eternia alone to retrieve the sword, they managed to merge the two universes into the same relative space. Once Mumm-Ra arrived on Eternia, he wasted no time in taking the form of the Sorceress, stole Prince Adam's Sword of Power and ended the young prince's life before the end of the series' first issue.

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He-Man Mumm-Ra Killed

Before succumbing to his wounds, Prince Adam was able to transform into He-Man and save his own life in doing so, but things didn't necessarily get better from there. Though Mumm-Ra would be reduced to ashes, his remains were consumed by Skeletor in a bid to increase his own strength. This led to the spirit of Mumm-Ra inhabiting Skeletor's mind alongside the Eternian villain's own, which in turn would eventually cause them to merge into a single impossibly evil foe for the heroes of both franchises.

Over the course of the crossover, the Masters of the Universe and Thundercats would come to visit one another's worlds in their quest to combat the forces of evil, and several of them would go through unbelievable changes of their own. He-Man's fearful feline companion Cringer would be transformed into ferocious Thundercat in the heat of battle, though that paled in comparison to the diminutive Snarf becoming a towering version of himself during the final fight against the similarly massive Ancient Spirits of Evil in the flesh. While the heroes proved to be victorious in the end, the damage done in the process from Prince Adam finally succumbing to his wounds to him being resurrected as a bloodthirsty beast were almost more than they could overcome.

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While later incarnations of both franchises strayed into darker territory, He-Man/Thundercats wasn't just a departure from the kid-friendly nature of these franchises and their original tone, it was easily the most brutal story that either team of '80s heroes experienced. Aside from the obvious caveats that come with any crossover such as this one, the frantic pace of both the story and action set it apart from any other incarnation of these classic series.

Masters of the Universe: Revelation has already shocked viewers more than once, but nothing it has done yet has been quite as surprising as seeing one hero graphically killed by the villain of another franchise in a twist that set the mood for the entire subsequent event series.

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