In the first film, “Star Trek: The Motion Picture,” a horrific transporter accident occurs in the first act. It’s kind of a plot point as the Chief Science Officer (a Vulcan we only briefly meet at Starfleet HQ) is killed along with another poor soul, necessitating Mr. Spock’s return to his seat. It’s fairly graphic, you hear screaming and see deformed humanoid shapes in the transporter “light show” on the ship’s platforms… the transporter technician says “oh no, they’re forming” shortly before what’s left of them is beamed back down to San Francisco. Starfleet ground control then confirms to Kirk and Co that “what made it back didn’t live long.”

Later (like only three or four scenes later), we are told that Dr McCoy doesn’t want to use the transporter to board the ship -likely because of the obvious inherent danger of the device- but is ordered to beam aboard by Kirk. His worry is then played for laughs… as if not an hour ago two people got melted and died. It’s a bizarre shift in tone, only made weirder by the framing of Bones as an old Luddite for being scared to use it.

Geordie: Reg, transporting really is the safest way to travel.

Reg: Didn’t one of them turn you into a ghost last week?

Well, it creates a copy of you in another place and renders the real you apart atom by atom. That’s pretty metal IMO.

No thanks

ENT did a little bit of body horror with the transporters since they were still new in-universe. One of the away team was beamed up during a storm, and some branches and leaves blew into the beam and became integrated into him when he rematerialized. He got better.

I’m hazy on the specifics, but in DS9, someone sabotaged the transporter and the contact they were supposed to meet burned alive during rematerialization. That was pretty gory for Trek.

Galaxy Quest went all the way and turned the pig-monster inside out lol … and then it exploded.