In the early days of Hellboy, Marvel superstar John Byrne brought his version of Spawn into the Hellboy universe. This was back in the days of Legend, a creator-owned imprint created by Dark Horse Comics as an answer to the wild success of Image Comics. Originally, John Byrne, Art Adams, and Mike Mignola were going to create a shared universe of characters including Mignola's Hellboy, Adams' Monkeyman and O'Brian, and the various titles created by Byrne such as Next Men, Danger Unlimited, and Babe.
Babe, written and drawn by John Byrne, was Byrne's return to the humor he was known for from his meta comic run on She-Hulk, albeit with more of a focus on story rather than jokes. Babe featured an Amazonian Redhead with the strength of ten or more men, and her quest to find out where she came from with the help of a sleazy Hollywood producer and an aged WW2 hero Blonde Bombshell. It even featured Abe Sapien and a cameo by Hellboy in its final issue. Babe only lasted 6 issues split between two mini-series.
While the series was more in the vein of Blackadder than the meta jokes of She-Hulk, Babe still featured some ribbing and sight gags that John Byrne is known to slip into his books time and time again. But none were more blatant or pointed than in Babe #3, with Byrne's inclusion of "The Jsedah Vvqevhds", a Wally Wood-esque martian dressed in a Spawn costume, one of a list of many insane and awesome versions of Spawn, albeit unofficial.
After Babe and crew ended up stranded on a hostile martian spaceship, The Jsedah Vvqevhds showed up to help them teleport back to Earth. He's only in a small handful of pages, and in only half of them, he is dressed as Todd Macfarlane's infernal avenger. In the story, the Jsedah Vvqevhds is a leader of the resistance, which may be a reference to Spawn being the lead book at Image, a company founded in resistance to Marvel. The Martians in Babe are led by a king who has mismanaged the martian people, firing or disposing of everyone who knew how to do their jobs and making everyone focus only on art. Eventually, there is no one left who knows how to use martian technology, with the entire race only having superficial knowledge. This seems like a cynical comment on Marvel Comics at the time, who seemed to value art over storytelling, and to some often displayed a lack of loyalty to the artists who helped build their empire, even leading to artists like Jack Kirby leaving for DC.
Byrne's inclusion of the Spawn costume also seems to be a comment from Byrne on his ownership over Spawn's design. In a letters column in the back of Babe 2 #2, someone comments on the Spawn costume, to which Byrne replies "Spawn costume? Gee, I thought I was doing the Nemesis costume, the one I created for Alpha Flight...". But the costume is unmistakably Spawn, with the Chains, Skull belt, leg pouch, spikes, and color scheme. There are absolutely similarities between Nemesis and Spawn, but Byrne has become known for his passive-aggressive digs with tongue in cheek. And that is how in a roundabout way, thanks to John Byrne, a wild version of Spawn ended up sharing a universe with Hellboy.