Are there higher CRs possible than the Tarrasque's CR 30?

Question

We were discussing with a DM friend of mine about the challenge ratings in D&D 5, and I affirmed the highest known to this day in the official content is the Tarrasque, with a CR of 30.

He then said that this wasn't true, and that there was some kind of "mythical" mode that could be enabled and which would include/allow even more deadly creatures. The problem is, he could not remember where he read that.

Did I miss something in the tryptic? Is it possible, RAW, to create monsters with a higher CR than 30?

Answer 1

Firstly, there are no official (as in, published by WotC) monsters with a CR higher than 30.

The rules for creating monsters are on page 273 of the DMG. While there is no explicit statement that monsters are limited to CR 30, all of the tables and rules for monster creation that depend on CR only go up to 30.

The DM can (as always) do whatever they want, but to create a monster with a higher CR than 30, they'll have to invent a lot of numbers. For example, the experience points for defeating it.

On the other hand, the hardest part about making a monster of CR >30 would actually be assigning it a CR. The majority of the monster creation guidelines are about assigning a CR to the monster.

To cut a long story short, whatever your friend is thinking of is either homebrew, 3rd party material, or something from a previous edition.

Answer 2

Your friend is thinking about rules from Pathfinder RPG, not D&D 5e.

So-called "Mythical" is an alternative name for epic levels used in Pathfinder. The point of epic/mythical alterations to monsters was to allow for PCs going above level 20 and still offering a challenge (but I would personally recommend against that in D&D 5e because the game at that point is not just completely out of balance, but also far, far beyond broken).

D&D 3.5/PFRPG can't be compared to 5e, they're just too different.

Answer 3

By RAW, you can create whatever you want as the DM. The only limitation is your brain.

DMG pg. 275 shows the CR rating for monsters you create. That whole section of the DMG actually covers how to build monsters. I know this answer is sparse, but generating a monster with a high CR is really easy to do. Take a Tarrasque and give it flight, and suddenly it goes higher than CR 30.