Let's see what the dragonquest.org has on
Murdaw…
…hmm, I have little idea what some of those numbers in the
Abilities mean since they're for a computer game.
It'd help if we had a monster with a clear 5E equivalent. It's inconvenient that dragonquest.org's
DQVI page doesn't have a table of monsters that appear in the game!
Let's try the Dragon Quest wiki… ah, that's more like it:
Many of these seem to be "inspired" by D&D monsters - the Porker is clearly some sort of Orc, for example. Oh, and we'll want the wiki's
Murdaw entry for comparison.
I'm seeing some common D&D monster names there: Shadow, Troll, Mimic, Gryphon.
Like most CRPG they come in various strength - a
Man-Eating Box being a weak version of a
Mimic, for example.
Let's see,
DQVI gives a
Mimic 304 hp (and the
Cannibox 144 hp), a
Troll 280 hp and a
Gryphon 200 hp.
In 5E, a
Mimic has 58 hp, a
Troll has 84 hp, and a
Griffon has 59 hp, so they aren't that far apart comparatively.
If we average the DQ Mimic/Cannibox's hp we get 224, pretty close to the DQ Gryphon's 200.
The ratio of geometric means of the two sets of hp (i.e. the cube-root of 280×224×200 divided by cube-root of 84×59×58) gives a ratio of 3.52, suggesting that one 5E D&D hit point is roughly equivalent to 3½ DragonQuestVI hit points.
Murdaw has 900 hp in his first and second DQVI encounter, so if that ratio applies (a BIG if!) he'd have about 257 hp in 5E, about the same as a
Balor but less than a
Pit Fiend.
That suggests he
might be equivalent to the weakest Demon Princes such as Juiblex, who is CR 19 in the 3E
Fiendish Codex I and CR 20 in the 3E
Book of Vile Darkness.
However, the
5E Juiblex is a more impressive Challenge 23 in
Mordenkainen's Book of Foes with 350 hp.
If you want to aim a little higher, the Challenge 24
5E Yeenoghu from the same source could also be used as a model for Murdaw's stats.
Anyhow, the first thing to do is decide on what Challenge you want this Dread Fiend to be, while leaving room for the more powerful fiends above Murdaw.