D&D 5E Advancing and Regressing monsters?

[RealMarkP]

I'm planning on running an evil campaign where the players start as Demons. Because there is a large variety of demons ranging from CR 1 to 20 (Balor), I'd like to select a few demon types, that are close to CR 5 and adjust them slightly so that they're either Advanced to CR 5 or Regressed from a higher CR down. Thus, the players would start with monsters that are of the same power level.

So, I recall 3.5 had rules for monster advancement, does 5e? And also, how would one regress a monster?

 

[Tormyr]

At any CR from 1 to 20, the easiest way is to modify their HP by 15 and their DPR by 6 for each CR level that you want to change it by.

For stuff around that CR, if they have a bunch of damage resistances adjust by 10 HP instead or 8 HP if they have 1 or more immunities.
If their primary damage is through spellcasting, then you may need to adjust spells to hit the change in DPR that you are looking for.

 

[Carnifex]

Yeah, *in theory* you can just shuttle them up or down the AC/HP/AB/DPR chart for creating new monsters in the DM's Guide. I'm not sure how well it'd work in practice.

 

[Tormyr]

Yeah, *in theory* you can just shuttle them up or down the AC/HP/AB/DPR chart for creating new monsters in the DM's Guide. I'm not sure how well it'd work in practice.

This is how I handled all of the solo monsters in my 5e Age of Worms conversion that is on this site when adding or removing PCs. For monsters from CR 1-20 with no resistances or immunities. In that case, because I did not want to adjust the damage of the monster (to avoid TPKs) I instead doubled the HP buff and added a bit more for being a solo monster against increasing numbers of PCs. In the end, 40 HP per PC above or below kept the difficulty of the encounter roughly as expected with groups of PCs up to 8. It was the result of 3 years of play from levels 1-20.

In a smaller set of cases, I modified both the HP and DPR to work adjust a weaker creature such as a goblin or lizardfolk. It works. The results are not perfect every time, but it is certainly good enough for these adjustments rather than recalculating the whole monster.

YMMV

 

[RealMarkP]

Excellent, I'll try this.

 

[Tormyr]

Excellent, I'll try this.

Just a thought...you may want to try your hand at building some PC race options instead. This would allow the players to still choose a class and advance in levels. You then do not have to worry about the CR of the monsters because the PCs were built like PCs.

* The marilith +2 Dex and can use her bonus action to make an additional attack and has as many reactions per round to parry as she has attacks + 1.
* The nalfeshnee +2 Int and can teleport 120 ft. as an action and can use it's horror nimbus 1/day.
* The Quasit +2 Dex and has shapechanger
* The vrock +2 Str and can fly.
etc.

Each of these can be a subtype of the Demon race which gives resistance to cold, fire, lightning and nonmagical weapon damage, darkvision 120 ft. and +1 to Con. The Subtype has a +2 in whichever ability score is the monster's best in the MM. This is real back of the napkin stuff. You would need to fine tune the race options a bit, but this would probably give you an adventure that behaved more like a regular D&D adventure in terms of ability scores, classes, skills, etc.