Splumonkeys are kind of the most obnoxious and unfun enemy I've ever seen in a game. But whatever, it's funny for some developers to troll their own playerbase.
I just had a playthrough that was game over'd in a single moment because the nightmare cycle started as I was entering the ruins, six Shadow Splumonkeys chased me, and I spent four minutes running all over the entire ruins trying to get them off me while gradually freezing to death because it was near winter and the cave rain had not stopped for over a day. So I died, because I literally had no way of surviving; I could not fight them because the horde was too large and would just stunlock me so I could not even attack, and I couldn't stop the damage ticking because anytime I tried to create a fire they would just hit me. And they chased me, for four minutes, through the whole ruins until I died.
What is the recommended strategy, never go anywhere near any Splumonkey areas when the arbitrary nightmare cycle that I technically cannot accurately keep track of without the medallion or a nearby fissure has reached the point where they turn into their Shadow form. So beyond how absurd that is, the recommended strategy for countering this content is to not associate with this content.
Don't Starve is a great game but Splumonkeys and especially Shadow Splumonkeys are just terrible, asinine game design which serves no purpose but to frustrate and potentially end the players game in ways they have almost no control of. I exclusively resent going to the ruins because of them. Two design elements you will not see done in any well designed game: enemies that never drop their aggravation regardless of what the player does, and enemies that stunlock players to the point of it not being possible to actually fight back. They combined both of these, into one enemy, then put that in a retail game; obstructing the entrance to one of the most important areas in the game.
If Klei seriously can't be bothered to make their own game fair then could somebody at least create a mod that nerfs Shadow Splumonkey aggravation. I would like the ruins to actually be fun.