I don’t know if the Summoner was hung or how he was killed.
Well, to be fair to Horuss and Gamzee they didn’t mean it maliciously; Horuss was severely infatuated with Rufioh and wanted to build him a new body but due to his immense hoofbeast obsession he made the body equine.
Gamzee on the other hand did try to kiss Tavros- not too sure why, be it from affection or the kiss of life. But he does mention in his log with Dave that Tavros was one of the few people who could’ve calmed him down from his rampage, which is why he found Tavros’ body first. Then Gamzee flies into his rage and kills Equius and Nepeta.
Horuss was clearly…half mad from his Page of Void abilities at this point and was very Otherkin/Horse-folk, so he wasn’t doing the horsebot thing maliciously; he legitimately thought it was the best form he could provide for his matesprit since he truely thought it was the most wonderful form you could become.
Gamzee was being fairly creepy, true, but he did genuinely care about Tavros and after finding him dead he decided to kill everyone. So yeah, at least he waited until after Tavros was dead to sexually assault him unlike Vriska…?