Calculating CR for a Full Caster Dracolich

[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.