Would an evil mage be able to spam fireballs in a combat encounter or would they run out of slots to use eventually?
[RPG] Do enethe NPCs have to use spell slots for their spells
dnd-5enpcspells
Related Solutions
Using Twinned Spell only uses one spell slot. This is because you are not casting two spells, rather you are making a single spell hit more than one target.
"...target a second creature in range with the same spell..."
However, it's worth noting that you can't cast Fireball with Twinned Spell.
Quote from PHB page 102 (emphasis mine)
Twinned Spell: When you cast a spell that targets only one creature and doesn’t have a range of self, you can spend a number of sorcery points equal to the spell’s level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip).
Don't apply a Limit Curse
I know this isn't the sort of answer you were looking for...but slapping restrictions on a player character because you don't like the way they are playing is not cool. The strength of a Warlock is that they get their spell slots back on a short rest. The weakness is that they only have a few. And the overriding weakness of spellcaster classes is that they have a limited number of times they can throw down heavy power. This is by design.
If the player decides he wants to waste all his spell slots on 'trash mobs,' then that's his call. It is not your responsibility to force him to be conservative with his spell slots. Nor is it your responsibility to save him from the fallout of his decisions.
That said, I will give you a few options.
- He dug his hole, let him lie in it. Stop nerfing the bosses. You are saving him from his own decisions by doing this. If you don't want PC deaths, you can still generally try to keep them alive, but stop compensating for his poor decision making. Play the monsters fairly. Honestly, he seems to want a tougher game than what you're giving him, he'll probably be happy if you hit him hard like that.
- That said, Warlocks have the best damage cantrip in the game. Even just spamming Eldritch Blast, they are quite functional. If they grab Agonizing Blast, they hit about as hard as your typical melee combatant does.
If you really want to show them the difference if the Lock has all his spell slots, then don't force him to conserve spell slots. Simply engineer a situation where they get a Short Rest right before a boss fight, so he can see the difference without you having to shove it down his throat.
But, ultimately, it sounds like he is playing his character the way he wants to and is having fun. So the final advice I would give is this...
Make sure he understands that the other players are not having fun (if they truly are not). If he likes 'the struggle' then perhaps give him other things to have to struggle rather than the one he is engineering for himself. Talk to him...see what he wants...make sure you guys are all on the same page.
Best Answer
Yes, NPC spellcasters (usually) use spell slots
This is covered by the explanation of monster attributes and abilities at the beginning of the Monster Manual. Spellcasting is covered on page 10 (emphasis mine):
In other words, they cast spells just like the PCs do, and their description will say which spells they have and how many slots they have. (For example, the Archmage NPC (MM, p. 342) is an 18th-level spellcaster with a list of spells and slots, e.g., they have four 1st-level slots.)
Innate casters are the exception
The “usually” covers the exceptions that don't use a Spellcasting feature. These are usually more monstrous critters that don't usually get called “NPCs”.
For example, a Pixie (p. 253) doesn't cast spells like a class and has no level, and has the Innate Spellcasting instead of the Spellcasting feature. Instead of casting using spell slots, they have “At will” and “1/day each” abilities that list the specific spells they can do on those terms. See the Monster Manual page 11, “Limited Usage” for details on these abilities.