The 5th Edition Monster Manual is a great book that’s filled with lots of lore and a wide range of foes for your party to battle. However, when you take a look at how the creatures it contains are distributed, it’s hard not to feel that drumming up enemies for tougher parties can get a bit difficult.
This is pretty obvious if you so much as glance at the official ‘Monsters by Challenge Rating’ PDF. The front page is stuffed with creatures with CRs of one or lower, and barely has room for half of the CR2 entries. Meanwhile, the second page covers everything up to CR15, and there’s less than a column left over for the truly high-powered monsters on the third.
In many ways this completely makes sense. After all, if there were high-CR creatures popping up all over the place the world would probably be scorched bare within a couple of days. Your average Kobold, Gnoll and Blight won’t be too much trouble for even fairly green adventurers, nor will the array of fairly mundane creatures listed at the back of the book.
Even from the perspective of game design it’s understandable that the amount of creatures drops off fairly quickly as CR climbs.
Technically once you get beyond CR7 or so creatures should be able to stand toe-to-toe with the most powerful adventurers out there. You really don’t need too many of them clogging up the book and taking space that could be devoted to monsters appropriate for parties in the conventional level 1-to-12 area that most games cover.
However, anybody who has actually DMed for high-level play will know that balancing can get a bit tricky once your players start getting to grips with their full skill-set. Individual spells can end battles on their own, while Action-Surging Fighters can deal ludicrous damage before combat even really begins. Having more high-powered options on the table could be useful for DMs unwilling or unable to start seriously homebrewing.
Beyond that, it’s hard to find a particularly diverse set of monsters beyond CR15 or so. Unless you want to be fighting a constant stream of Dragons things start getting very sparse indeed. If you don’t feeling like having your party get involved with Planer matters and start battling Angels, Devils and Demons either you’re basically out of luck.
It’s rare for parties to keep playing at high levels, and to be honest most groups will be more than happy with the traditional Fiendish and Draconic enemies on offer. However, it would be great to see a little more diversity introduced to the line. Volo’s Guide to Monsters went some way to addressing this with creatures such as Alhoons and Giant specialists, but the top-end of the CR chart is still pretty empty.