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Fireball & Lightning Bold Ruin Encounter Design - What DMs Get Wrong

Tenkar's Tavern

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There are exactly two walls every B/X campaign hits: the Magic-User getting Fireball and Lightning Bolt at level 5, and one level later, the Cleric getting Cure Disease, Remove Curse, and Striking at level 6. Both moments change the math behind every encounter you've already built — and most DMs get caught flat-footed because nobody frames it as a design milestone instead of a balance problem. In this one I break down exactly where these walls sit, what they do to your monster math, your corridor geometry, and your cursed-item plot hooks, and how to redesign past them instead of taking spells away from your players.

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00:00 Why 3rd Level Spells Break Low Level D&D Encounters
02:44 The Level 5 Magic-User and Level 6 Cleric Walls
03:13 Fireball Damage Math vs Low Hit Die Monster Mobs
04:32 Lightning Bolt Dungeon Geometry and Corridor Rebound
05:20 Cleric Cure Disease and Remove Curse Spell Impact
06:50 The Cursed Magic Weapon Campaign Mistake
08:54 How to Design D&D Dungeons for 3rd Level Spells
10:52 Tactical Corridor Layouts and Dungeon Architecture
11:39 Preparing for Cleric Curse and Disease Removal
12:30 How to Audit Planned Encounters Before Level 5

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20 Comments

@TenkarsTavern Creator 3 months ago Pinned

The fix is never “ban Fireball.” It's building a dungeon that has more than one way to threaten a party that just earned the spells to beat the old one. What's the worst time a spell like this ever wrecked one of your encounters? Tell me below — I read all of these.

@briansmaller7443 3 months ago

I remember TPK on our whole party when the fireball went off in a room - and we forgot the volume rules. Sad - but funny as all hell.

@Jonathan-z6e4v 3 months ago

After months of play, hiding at the back, throwing darts the wizard finally gets to shine at 5th level - but only once a day and then there are the constraints of fireball burst volume and for lightning bolt ricochet.
Celebrate the fact that spell casters get a bit of power

@trevynlane85 3 months ago (edited)

It is something to keep in mind. I put enough Fireball worthy encounters to equal 25% more than the available spell slots for that spell. That keeps the power boost of the spell useful, but still makes it not the be-all end-all for the party. If they have it, expect them to use it!

@ForeverYoungKickboxer 3 months ago

Running B10 for the BECMI campaign I DM, there's an encounter where you can rescue slaves and horses from an encampment of Iron Ring slavers. The magic user dropped a fireball indiscriminately into the camp and ended up roasting 9 of the prisoners alive along with most of the Iron Ring. There was one survivor who stopped in front of a charred body, then snatched a knife off a dead burnt goblin, fell to his knees and slit his own throat, turns out the deceased was his wife, so a total of 10 innocents lost their lives that day. It was an ugly scene and the party nearly came apart at the seams.

@SimonAshworthWood 3 months ago (edited)

Mage spots 12 kobolds. “I cast fireball”

Mage loses initiative to some of the kobolds. Mage is hit by 5 arrows and becomes human pincushion.

@tomyoung8563 3 months ago (edited)

I love it when they get fireball! The players are excited and it doesn’t jam me up at all because I know infantry tactics plus I don’t play the monsters like they’re stupid

@chriswarner8906 3 months ago

Fireball is just higher level sleep. It's fine. Cleric spells, though? Those things are crazy

@garrickstangle5996 3 months ago

Last session my party ate a fireball on two separate occasions. They REALLY don't enjoy being on the wrong end of the fireball.

@sebbonxxsebbon6824 3 months ago

Fireball, the reason everyone who started D&D with us had a fighter as his first character, no exceptions.

@angryman2406 3 months ago

One way I look at it is that although they may have blown up 20 goblins with that fireball and cleared the room without even fighting, that casting of fireball is gone for the day; they may be able to keep that momentum going for a bit depending on how many fireballs the mage has, but they will run out if they keep on clearing rooms like that.

@sebbonxxsebbon6824 3 months ago

If as a DM you can't handle fireball, wait until you have a 18th level cavalier with a rod of flailing, a girdle of storm giant strength, a +3 hand axe, and he attacks 8 time and does 150 damage in one round.

@Ijimisan 3 months ago

Much like briansmaller7443, the volume rules quickly disabused us of fireballing all day every day when underground or indoors. Never had a TPK as a result of it, but one time I did kill half the party.

@tonyc196 3 months ago

I plan adventures FOR fireball.

My PCs recently found the cult hide out. 25 cultists of various classes ranging from level 6-9. There was at least three fireball/lightning bolts. There was a cone of cold. There was flanking and sneak attacks. There was bombs (we have an alchemist). The players trying to track which cultist was which class. It was pure chaos.

Damn I loved that encounter.

@notreallydavid 3 months ago

One option: a chain of encounters that come at the party in rapid succession with little scope for disengagement and withdrawal. The party might use their one-only third level pride and joy on the first group of bugbears, but they're compelled to find other means to deal with the second bunch that immediately come at them from a side passage. Or the third squad that set up an ambush position along the party's route to safety.

@S.C.A.-T.S.R 3 weeks ago

Fix a bead of force on your heavy crossbow bolt.

@JosephHeller-el8zo 2 months ago

Illusions are the counter to fireball spells. And not just magical illusions. A fireball cast into a room full of bugbears can turn into a trap. Make the room small, maybe only 10’ wide, and have the walls shaped and painted so the room looks larger than it actually is, then have lifelike puppets of a horde of monsters waving arms aggressively. When the Magic-User hastily casts fireball into a 10’x10’ room he roasts himself and anyone near him…

@Emanemoston 3 months ago (edited)

My buddy played an Eleven magic-user thief, he finally levelled up and got his fireball. After a few runs he said he regretted it, there were just so few chances to use it, while he could have all those other spells instead. Was really fun the two times he got to let it off the chain though.

@jamesbennett9264 3 months ago

As the DM you have complete control over what spells your players find and are able to transcribe into their spellbooks. I like to have my players find some of the lesser used spells first and give them a chance to be creative with those spells. In my current group the Wizard only has explosive runes and clairaudience as the only 3rd level spells in her spellbook and it has been great fun watching her creatively use these spells to great advantage.