How many of my daily spells should go into purely defensive spells?

[heavyfuel]

For example, a lv 6 Druid only has 3 lv 3 spells.

While a spell such as Heart of Water is potentially amazing and life saver, if you don't encounter a situation where FoM is useful, you've spent 1/3rd of your highest level spell for nothing.

This argument can be made for plenty of defensive spells, from pretty much any spell level (except maybe 0 and 9)

So yeah, if you don't know what situation you're facing, how much should you invest in defensive spells?

[Elkad]

I don't think you can make a rule of thumb for that, it depends too much on the rest of the build, and the rest of the party.

If you spend the day orbiting the ground-bound party on your giant bat companion, you may not use any of your high-level slots on long-term (cast before the fight) defenses.
If you spend the day wading into combat in bear form, you might spend quite a few of them, especially since they are shared with your bear companion.

I know on a pretty standard conjuration wizard, I dedicate maybe a third of my spell slots to defenses. Half of those are long-term. A good chunk of that is so the buffs are shared with my familiar, who tends to be at a higher risk than me. I can usually get by with careful positioning, and the occasional tactical teleport (likely off a wand). I don't use Heart of Water without a specific reason until about 9th level, it's just not that useful.

[sleepyphoenixx]

Like Elkad said, it depends on what you're doing. If you're doing the Bat thing you'll want to use your high level spells for offense/BFC.
If you're doing the beatstick thing you already have offense and can't use most forms of BFC without running into them yourself anyway.
This trend continues throughout your career. If you're getting the majority of your defense from your wildshape form you need less spells for that. If you're using a high AC form you don't need to cast Barkskin. If you're a Fleshraker you don't need any damage spells beyond Venomfire (if that).

There's also the fact that some roles don't need your highest level spells.
Entangle or Impeding Stones are still plenty useful at 6th level, so you can use your 3rd level spells for other things.
A Ring of the Beast means you never have to use your highest level slots for summoning, plenty of buffs scale with CL and so on.
Also consider what effects you can get from summons - there's generally no need to prepare those when you can summon spontaneously.

You can also experiment to find what works for you/your table. Try different wildshape forms and if you take too much damage switch to another.
Prepare some defensive spells and only cast them when you think you need them. Otherwise you can just use them to summon and prepare something else the next day for any that are excessive.
Last but not least most campaigns at least have a general theme, so unless your DM just throws a bunch of random encounters at you you should have at least a general idea of what you need.

[Fizban]

If you don't know what you're facing, you take a guess and prepare the defensive spells that are widely applicable or which your party is particularly lacking in. How many depends on how much of a team player you are vs how aggro you are. If you're actually preparing major defensive spells for the party, you'll need anywhere from 1-4 copies of each spell depending on formation, terrain, and number of foes, if that spell comes up. But since you don't know what you're facing, you'll probably try to make do with just 1-2 of each major immunity.

Anything more than one defensive and one offensive buff starts becoming a hassle and overshadows the person the buffs are on, but depending on encounter clustering you might prepare extra copies for later encounters.

Druid 6? A Mass Resist Energy or Neutralize Poison (or both) should be ready, then probably a couple Barkskins for value or extra Delay Poison/Resist Energy (or Body Ward, which works vs poison and Shadows), and maybe some Delay Disease or Endure Elements- those last two are much better on scrolls though. A Cleric would be packing Magic Circle, and if there's water then Water Breathing is probably a good idea.

The elephant in the room is personal only buffs, the Heart of Water you just made example of. If the party is a group of individuals using personal-only buffs, then you prepare enough to last you all day, however many that means to you. The Heart of X spells only trigger their big effect once, but the only one you're likely to trigger every fight is Heart of Earth (maybe Heart of Fire). A Druid 6 would prepare Heart of Water if there's water around or they're particularly afraid of grappling, but otherwise they're still gonna want that energy/poison/ability damage resistance.

[ayvango]

Defensive spells are always good. Offensive spells could be replaced with wands/staffs. They surely consume wealth, but get you steady progress. If you use 4 charges to defeat appropriate monsters then 40 charges is level and enough loot to buy another wand.

[Kurald Galain]

Defensive spells are always good. Offensive spells could be replaced with wands/staffs.

That doesn't work too well. Wands usually have only the minimum caster level and save DC, meaning they are much better for defensive spells instead of offensive ones.

[Red Fel]

Defensive spells are always good.

I disagree. With the exception of defensive spells designed to protect against environmental hazards, the general rule is that the best defense is flat-out murder. A dead enemy can't harm your party. If we're talking about truly optimizing spell selection, the goal is to bury your opponents as quickly as possible to prevent damage from happening in the first place.

Defensive spells can be pierced or dispelled. But dead is dead.

Now, that's not to say that this is an optimal playstyle. A caster who acts as a force multiplier instead of a mobile death platform is still awesome. But in terms of whether defensive or offensive spells are better, there is an objective answer.

[sleepyphoenixx]

Defensive spells are always good. Offensive spells could be replaced with wands/staffs. They surely consume wealth, but get you steady progress. If you use 4 charges to defeat appropriate monsters then 40 charges is level and enough loot to buy another wand.
Defensive spells are always good until you have enough defenses. After that they're wasted slots. Pumping your AC to 60 doesn't do anything if the enemies you're facing can only hit AC 45 on a natural 20. Being immune to fire is completely useless if you're not fighting enemies that do fire damage. Freedom of Movement only helps if your enemy is actually trying to hinder your movement.

Frankly a druid doesn't need much in the way of defensive spells as long as they pick an appropriate wildshape form, at least not at level 6.
You can if you're content taking the melee role, but if you're doing BFC you're not only preventing yourself from being damaged but also your party. If you're hiding behind summons you'll rarely get attacked in any significant way. And so on.

Wands lack CL and save DC's. They're best used on utlity spells or those few defensive spells that don't need a high CL for duration.
If you want to use wands offensively you need to specifically build for it (Artificer, Cannith Wand Adept, Wand Mastery, Enhance Item etc). It's not something you can just pick up as a sideline.

Staffs are hideously expensive, even lower level ones. And those have dubious usefulness. Their price is in no relation to their actual combat value. Even so, by the time you can afford one you're pretty much beyond the "not enough spells" phase.

If you find yourself lacking in spell slots you're better of buying Pearls of Power, a Ring of Wizardry (if applicable) or pumping your casting stat.
Or changing up your spell selection, because generally by the time you can afford to splurge on spell trigger items you should have enough spells to last you a normal adventuring day.
This applies double for druids who can cover at least one aspect of their repertoire with wild shape.

[ayvango]

the general rule is that the best defense is flat-out murder
Wands is sufficient for that part.



A dead enemy can't harm your party.
Unless he managed to surprise your party or win initiative roll. And in that case without defences you would be dead and harmless.



Defensive spells can be pierced or dispelled

And that would win you round or two to kill your enemy.

That is all about economy. In most cases battle begins with ambush. You should prepare beforehand for it. But you are always uncertain would you face real danger today or net. Spending magic wands on defence possesses innate economical risks: what if you would not have chance to use it today? Therefore is better to prepare defences on everyday basis and use offensive wands on demand.

The special case is prepared battles. When you had prior knowledge where would the battle hold, who would be engaged in it and what are their abilities. In that case it is more rational to prepare specific spells that are not stored in wands. Specific offences, specific defences, or even specific battlefield changers like stone shape, if you plan the battle ahead and found a cunning way to use your spells effectively.

Such battles are rare cases. You need to deliberately spent a lot of time for gathering intelligence instead of just beating someone faces to collect XP. Another way to know your enemy beforehand is to face him early and taking decision to flee instead of fighting. It's perfectly normal: your own safety has higher priority then gaining XP, and if you anticipate defeat you should disengage early. But it still unlikely, most normal challenges are typically affordable for a party. And if party engages enemies it leaves no one alive.

I'd like to say it twice. You are needed to blown your opponent either way. But spending spell slots for defences and wands for offences is economically advantageous. Because for every wand usage you get immediate benefit in XP and loot. And you could do more wands with it. You could take as many encounters a day as you have wand charges. Spell slots are irrelevant and should be used for utility and special cases.

[ayvango]

Being immune to fire is completely useless if you're not fighting enemies that do fire damage. Freedom of Movement only helps if your enemy is actually trying to hinder your movement.
Do your enemies give you warnings before the day that they would like to attack you and list would-be used weapons of destruction?

You should plan ahead and make some reasonable assumptions.

[sleepyphoenixx]

Wands is sufficient for that part.
Except they're not. As has been pointed out wands have minimum CL and save DC. You won't kill or hinder anything with that in a reasonable timeframe.
If you insist that you can i'd like an example of what spells you're using.
Because it's a simple fact that by the time you can afford a wand of them 1st level damage spells are already too weak to be worth using in a level appropriate encounter even with scaling.
The same applies to higher level wands at later levels.


Do your enemies give you warnings before the day that they would like to attack you and list would-be used weapons of destruction?

You should plan ahead and make some reasonable assumptions.
Does nobody in your games scout? Ask around before going on a mission? Use divination spells?
Sure, you can sometimes be surprised, but from some people here you'd get the impression that DM's commonly roll encounters completely randomly from the various MMs instead of having a cohesive campaign.

I'm not saying don't use defenses at all, but after you've covered the "instant death" conditions spending more is just wasted.

Fact is that you'll never have enough spell slots to be immune to everything during normal play. This applies double to lower levels where spell slots are limited enough that you can barely cover one or two weaknesses.
As i mentioned above using BFC to lock down an enemy prevents him from damaging you (and your party) much more effectively than trying to cover every defense.
Thus the best defense is a high initiative combined with good BFC.

This isn't my secret way of winning D&D btw, it's common knowledge that going first and using BFC rules 3.5 combat.