On to fiends, which receive—by far—the greatest number of substantive changes in Monsters of the Multiverse, and that’s not even counting archdevils and demon lords. In fact, so many fiends receive significant updates to their actions that I’m going to break my examinations of this creature type into five posts: three for the rank and file (one each for the lawfuls, chaotics and neutrals) right now, then two more for the archfiends (one for archdevils, one for demon lords) after I’ve covered all the other creature types.
To begin with, the merregon’s Multiattack has been made unconditional: three Halberd attacks, period, whereas before it received the third only if there was a superior devil within 60 feet of it. That means there’s no longer any particular need for merregons to form a line to either side of a bone devil, erinys, pit fiend or amnizu commander. They can form any kind of formation now, including rank upon rank in front of their commanders, who can lead from the rear. A detachment of them can also break formation to strike at an enemy weakness. Mind you, at CR 4, merregons are hardly weak minions—each of them is roughly the equivalent of a level 11 PC—so even a mere platoon of them is better managed using the mass combat rules of your choice. The Loyal Bodyguard reaction is unchanged, so it does still make sense for a ring of merregons to surround the superior devil that commands them and act as its personal guard.