How do players defeat the coin dragon in Gorgoldand's Gauntlet?

Question

There is a one-shot adventure called Gorgoldand's Gauntlet, originally designed to be run with 3.5 rules.

The adventure mostly consists of a series of puzzles, traps, and a few encounters. However, the climax of the adventure has the players fighting a "Coin Dragon". After reading through the adventure, it does not seem to indicate a way that a group of characters can kill the dragon.

Most ordinary weapons do little or no damage to the coin dragon. Piercing and slashing weapons slide right through the loose objects in its “body,” doing no damage. A blunt weapon like a mace or club might dislodge a handful of coins, but these are easily returned to the coin dragon the following round. (They are sucked back into the creature’s body telekinetically.) A dispel magic cast upon the creature causes the disparate objects forming the dragon’s body to crash to the floor, leaving the dragon “bodiless.” The creature reforms its “body” the following round, but this allows PCs time to escape (possibly with an item or two from the hoard). The coin dragon is not permanently destroyed until it loses all of its hit points. The coin dragon never leaves its treasure room and naturally heals 3 hit points per day. PCs in combat with a coin dragon might find it necessary to do some damage, leave the treasure room to heal up and prepare new spells, then continue the assault later (possibly over the course of several days, depending on the strength of the party).

SQ—Construct: Immune to mind-influencing effects, poison, disease, and similar effects. Not subject to critical hits, subdual damage, ability damage, energy drain, or death from massive damage.

SQ—Resistances (Ex): The coin dragon has acid, cold, electricity, and fire resistance 5.

If I'm reading this correctly, it seems like any weapon attack with non-magical weapons are easily shrugged off. It looks like it's possible to deal magical damage to the monster, but it appears to be immune or resistant to most kinds of damage.

This is an encounter designed for a group of 1st level players. Given that spell casting is limited at 1st level, or that a party might not consist of an offensive spell caster, how is it possible to defeat this foe? Specifically, as the campaign was written, how was the foe intended to be defeated, or is it not intended to be defeated?

Answer 1

Damage it a bit and run away to come back later

It only heals 3 hit points per day so if you can use your spells to do more than that much on average day (which shouldn't be hard even at level 1), you can kill it over time. This is specifically called out in the description:

The coin dragon never leaves its treasure room and naturally heals 3 hit points per day. PCs in combat with a coin dragon might find it necessary to do some damage, leave the treasure room to heal up and prepare new spells, then continue the assault later 

You probably need Magic Missle since its the only damaging level 1 spell that the dragon doesnt resist. Otherwise, this will be very difficult as the only way level 1 characters can damage him effectively is through perfect rolls on Shocking Grasp or Chill Touch (which can deal 6 damage on a maximum roll beating the 5 resist)

Answer 2

Note: I've only read the dragon's entry in the linked PDF, not the whole adventure.

As David Coffron said, kill it incrementally. The dragon heals 3hp/day, has DR 10/+1, and resist all relevant elements (that is, all elements that can be used to cause magical damage in the core book with 0th and 1st level spells) 5 and 18 hp.

As mentioned, Magic Missile will do straight damage to the dragon.

Let's posit, though, that there's a Barbarian in the party who rolled well, so has an 18 STR and is using a two-handed Greatsword (2d6 damage). That's 2d6+6 damage, for an average of 13 per round (1d6 averages 3.5, 2d6 averages 7, + 1.5x STR). The barbarian can Rage for a few rounds, adding +4 to STR, so +3 to damage (thus, averaging 16 damage per round). At this point, the barbarian is, on average dealing enough damage per attack to negate two day's worth of "fast healing".

But, wait: there's more!

Someone can cast Magic Weapon on our barbarian's sword, thus adding another point of damage (average 17). At this point, the barbarian's average damage is 17 (minimum of 11), and is bypassing the dragon's DR (since the sword now has a +1 enhancement bonus, and thus bypasses DR/magic).

Some monsters are vulnerable to magic weapons. Any weapon with at least a +1 magical enhancement bonus on attack and damage rolls overcomes the damage reduction of these monsters.

-- SRD

Two hits from the barbarian, and the dragon is no more. And one hit wouldn't be shocking.

Meanwhile, the druid can cast Shillelagh, and their quarterstaff is now a +1 weapon dealing 1d10 damage; even with a +0 STR, that's an average of 6.5 damage per round; if they're hesitant to enter melee, they can also pair up with the cleric to cast Magic Stone, and start throwing rocks for 1d6+1 damage (again, bypassing the dragon's DR); it's only 3 rocks each at an average of 4.5 damage per rock, but it's still 13.5 damage per character.

Magic Stone lasts 30 minutes, Shillelagh and Magic Weapon both last a minute per level, and raging is a free action which lasts for 3+CON rounds at a time (including the CON bonus you get for raging, so it's almost guaranteed to be more than 5 rounds).

So, the cleric casts Magic Stone and prepares to throw rocks or provide healing. The druid and the wizard cast Shillelagh and Magic Weapon (respectively) as the barbarian prepares to rage and charge the dragon while the cleric opens the door. The PCs win initiative, so the barbarian rages and charges, taking the dragon down to 4 HP. The cleric throws a stone and misses, the wizard casts Magic Missile and rolls minimum, bringing the dragon to 2 hp, and the druid charges in with her quarterstaff and finishes it off.

With a full spell list (and a little luck with the dice, of course), it's not hard to see the party finishing the dragon off before it gets to act.

Answer 3

There is a time-honoured technique in D&D for dealing with monsters that are not vulnerable to normal weapons, which is to hit them with magical ones. A +1 weapon is sufficient to overcome the damage resistance, and there are several thoughtfully provided in area 13.

If your party isn't powerful enough to take it out in one combat you can back enough, heal up, pick your most suitable spells and go for another round.