Calculating CR for a Full Caster Dracolich

[othaero]

So my party will be raiding a Drow temple to stop what they (and the drow) think is a ritual to bring Lolth into the world. In reality it is a Dracolich fooling the Drow into thinking He is Lolth trapped in a gem (his phylactery). So I end up picking the type of Dragon I want to be the Dracolich and give it spellcasting according to the rules in the MM but I feel like it doesn't really capture the feel of a Dracolich (something like only 5 spells 1/day). If I wanted to give it full spell casting (focusing on mostly enchantments) how would that affect the CR?

[Lolzyking]

perhaps base it on a weaker dragon, boost the health and ac, but not its damage as much to make it a stronger caster

[LeonBH]

That depends on the spells you give it.

[othaero]

I was thinking of giving it the spell casting of a level 7 Bard with the following spells

Spoiler: Level 1 Spells

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Charm Person, Silent Image, Sleep

Spoiler: Level 2 Spells

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Hold Person, Invisibility, Silence, Suggestion

Spoiler: Level 3 Spells

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Hypnotic Pattern, Major Image

Spoiler: Level 4 Spells

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Confusion

Party Comp (if it matters/if you think this might be too strong) all level 8 in a High Magic/High Stat Campaign
Dragon Sorcerer, Bear Barbarian, BM Fighter, Assassin Rogue, Lore Bard, Life Cleric

[LeonBH]

Based on that spell selection, I don't believe the CR will change at all. You're looking for explicitly offensive or defensive spells to change the CR, like Disintegrate or Shield.

[othaero]

Appreciate it, though I'm sure my player's won't

[UrielAwakened]

Fun fact about the CR system - It's really dumb.

The only factors that increase or decrease CR are HP, AC depending on your HP, Damage, to hit bonuses/spell DCs based on your damage, and traits and abilities that somehow modify these effective values (such as a way to regularly acquire advantage on all of your attacks, or regeneration, or a lot of common damage type resistances.)

By the book, knowing Wish does not improve a monster's CR at all.

This is what you do:

Figure out what its 3 most damaging spells would be (The damage calculation is always based off of just the first 3 rounds of combat).

Calculate what their average damage is going to be, based on how many targets you expect to it (so for instance, Meteor Swarm will probably hit all 5 people in a 5-person party. That's an average of 140 damage, 5 times (so 700). Don't forget to include out-of-turn actions too, like legendary action attacks you expect it to make.

Average it across 3 rounds (so if a monster did Meteor Swarm once, then resorted to nothing but bites and claws that do an average of 40 damage per round, its damage total would be 700+40+40 all divided by 3, or 260.

Find where that puts it on the custom monster CR tables.

If you aren't changing its HP or AC, just average the Offensive CR and Defensive CR at this point. However if you're giving it something like Shield, you have to treat its effective AC as 5 higher and recalculate that too.

Now as I said, that's how CR SHOULD work, but the CR system is really dumb.

Instead I would treat any spell that incapacitates a creature as a spell dealing the same damage as an average PC of the monster's level. If it requires concentration, treat it as half damage.

So for instance, Hold Person would add half of the average PC HP to its damage output per round. This gives you a more full representation of the threat the monster presents.

[PhoenixPhyre]

Based on that spell selection, I don't believe the CR will change at all. You're looking for explicitly offensive or defensive spells to change the CR, like Disintegrate or Shield.

Right. CR depends on using the best offensive actions (averaged over 3 rounds) and things that explicitly change AC/health/damage intake. This means that "soft" spells don't change CR. They do change the effectiveness, but that strongly depends on the rest of the encounter. Giving control spells to a solo beast makes less of a change than giving control spells to a minion-mancer whose minions can take full advantage of the crowd control.