Advancing Monsters?

[flameboy99]

I've decided for the campaign arc I'm running, I'd like the Big Bad be a Yuan-Ti Pureblood with some additional casting abilities. However, I'm not really sure how I should go about this. Unlike 3.5 (Which is what I'm used to), there wouldn't appear to be any rules for advancing monsters, or at least I haven't found them if there are. Should I fully homebrew the stats, based off of the Yuan-Ti Pureblood stats? Should I just apply the appropriate class abilities of, say, a warlock? Something else entirely?

[Kd7sov]

They're in a tiny little section on page 283 of the DMG.


You can use the rules in Chapter 3 of the Player's Handbook to give class levels to a monster. [example involving a "Werewolf, 4th-level Barbarian"]

Start with the monster's stat block. The monster gains all the class features for every class level you add, with the following exceptions:

The monster doesn't gain the starting equipment of the added class.
For each class level you add, the monster gains one Hit Die of its normal type (based on its size), ignoring the class's Hit Die progression.
The monster's proficiency bonus is based on its challenge rating, not its class levels.


Once you finish adding class levels to a monster, feel free to tweak its ability scores as you see fit (For example, raising the monster's Intelligence score so that the monster is a more effective wizard), and make whatever other adjustments are needed. You'll need to recalculate its challenge rating as though you had designed the monster from scratch.

The CR-calculation rules and table, in case you're now looking for those, are on page 274.

[Tenmujiin]

It is best to make a homebrewed monster based on the creature you want to advance using the monster creation rules in the DMG p.273. Advancing monsters are PCs in 5e can result in weird power levels and PC levels don't translate directly to CR.

Edit: if you want to increase its spellcasting, also increase its HP, AC and/or stats to make sure it isn't too squishy and then recalculate its CR based off the table on DMG p.274