Spells

Set the creature's spell DC and spell attack modifier using the Spell DC and Spell Attack Modifier table. Most creatures use the same DC for all their spells, even if they have multiple types, such as a creature with both prepared spells and innate spells.

Use the high numbers for primary casters, and the moderate numbers for creatures that have some supplemental spells but are focused more on combat. At 15th level and higher, the extreme numbers become standard for spellcasters. A few creatures might use the extreme numbers at lower levels, but they tend to be highly specialized, with very weak defenses and Strikes. Secondary spellcasters can go up to high numbers if they're above 15th level and have offensive spells. There's no low value—the creature shouldn't have any spells in the first place if it would be that bad at using them!

Spell slots work best for creatures that are meant to play like PC spellcasters. Choose the magical tradition best suited to the creature. You aren't strictly limited to that tradition's spell list, though sticking close to it will make your creature's connection to that tradition clearer. The decision to use prepared or spontaneous spellcasting should align with the creature's theme: a spontaneous spellcaster fits well as a one-off creature since spontaneous spellcasting grants greater flexibility in the middle of battle, while a prepared spellcaster makes for a great recurring character who can change their spells between appearances.

For a creature that can cast as many spells as a PC spellcaster, the highest spell rank the creature can cast is half its level rounded up. It gets five cantrips. If the creature's level is odd, it gets two spell slots of the highest spell rank (plus three spell slots of each lower rank), or three spell slots of that rank (plus four spell slots of each lower level). If its level is even, it gets three spell slots of the highest spell rank (plus three spell slots of each lower rank), or four spell slots of that rank (plus four spell slots of each lower rank). You can base the number of spells on the class you're trying to emulate or choose more spells if the creature doesn't have many other abilities.

Because creatures tend to be “on stage” for only a short time, you usually don't need to fill every spell slot. You can often fill just the top three ranks of spells, pick cantrips, and slot in a few thematic backup spells in the fourth rank down. For a recurring foe, you might give it a full complement of spells.

Unlike prepared and spontaneous spells, innate spells can be of higher rank than half the creature's level rounded up, and you can choose how often they're used—they can even be used at will or be constant effects. The most notable innate spells tend to be top-rank ones that make a big impact but can be used only once, at-will spells that strongly reinforce the creature's theme, and constant spells that give it an ongoing benefit. A spell that's usable a limited number of times and has a lower rank than the creature's highest rank is typically less likely to come up in combat; however, that's a great spot for utility and recovery spells, such as delete or personal gravity.

Sometimes a strongly thematic innate spell is of a higher rank than the creature would normally be able to cast, but it's so fitting that it belongs there. Be careful when doing this, as PCs might not have access to the appropriate countermeasures for the spell. This option works best for support, action denial, or battlefield control spells that change the odds of a fight without outright killing anyone, such as the alghollthu omnipath's dominate spell. These should make the fight more interesting, not end it. Keep the number of such spells very low, typically just one.

Though you can achieve all sorts of things with innate spells, always start with the theme and an idea of how you want the creature to spend its actions. And though you could give the creature a tool to counter every kind of PC attack or trick, remember that the players chose those options to enjoy using them, rather than to be constantly foiled by an effectively invincible creature.

Since rituals happen during downtime, giving them to a creature is usually a purely thematic choice. You can skip even looking at rituals in most cases. If you decide a creature needs to have a ritual for your story, add in the ritual whenever you need it.