Broadly counted every instance of rape, murder, and nudity in "Game of Thrones." An introduction to this data and methodology can be read here, along with the total numbers across all seasons.
Notable deaths: Mance Raydar, Janos Slynt, Barristan Selmy, Maester Aemon, Shireen, Stannis, Meryn Trant, Jon Snow, Myranda, Myrcella
Notable rape scenes: Sansa (Ramsay)
This was one of the hardest seasons for me to re-watch, and I'd recommend skipping it for a few reasons. Though this wasn't the Deadliest Season (second to season 7), it was the first time that women's onscreen death numbers were in the double-digits—a big difference from seasons 1 and 2, which only showed one woman's death each. And although it didn't have the most rapes, it did have one of the most criticized rape scenes in the show's history. Most offensive, this season introduced the most frustrating female characters of the entire series.
The Sand Snakes are a Dornish trio of Oberyn Martell's bastard daughters, trained extensively in combat by the famed and deadly fighter nicknamed The Red Viper. Despite the fact that this sounds objectively cool, every scene with them is pretty much unviewable, and their character arcs make no sense: What's with their inconsistent, indistinguishable accents? Why would they feel that a logical way to avenge their father's death is to kinslay his kind brother and innocent nephew? Why would sisters insult each other with the word "slut" in a libertine kingdom where overt sexuality, incest, or bastardry aren't frowned upon? Why would anyone ever utter, as Tyene did to Bronn: "You want a good girl but you need the bad pussy"?!
In Episode 6, Sansa is brutally raped by Ramsay while Theon watches, a non-canonical event that was universally panned, with George R.R. Martin going out of his way to say it won't happen in "A Song of Ice and Fire." Though this season caught the worst flack from critics for Sansa's rape, Season 5 is also notable for being the second deadliest (the first being Season 7), but feeling like the deadliest. Multiple battles claim dozens onscreen: The Unsullied face off against the Sons of the Harpy, Wildlings are massacred by the Army of the Dead at Hardhome, and Stannis's forces are soundly defeated by the Boltons.
"Hardhome" is my favorite episode of the series (and one of its best rated on Rotten Tomatoes): When Jon teams up with Tormund Giantsbane to make peace with the wildlings, we finally see the scale of the battle between the living and the dead. Thousands of freefolk are massacred, but we are introduced to the only other wildling warrior woman we meet besides Ygritte. As she assured the passage of her children to safety, she seems set up for a longer character arc. But of course, she dies within minutes.