If you've just attempted to fight Fire Dragon Mauna for the first time and been burned to a crisp, you're probably thinking something like "is this optional fight even worth it?" Unfortunately: Yes. Winning here is very much worth the reward, because beating this boss will provide you with what is inarguably the best early game weapon you can find in Metaphor: ReFantazio.
Fortunately there's a straightforward method to beating Fire Dragon Mauna without hours of grinding, but it does require spending a little cash.
Metaphor: ReFantazio's optional dragon boss guide
There are two ways to take down Metaphor's optional early dragon boss. First, and the one I recommend, is splashing some cash to shortcut your way to the win. The second approach requires changing all three of your party members' Archetypes and doing some (but not tons) of grinding.
If your coffers are empty it might be your only choice, but I suggest saving up enough money to buy your way to an easy win.
How to beat Fire Dragon Mauna the easy way: Using Ice Chunks
Prior to the fight with the Homo Fulquilo earlier in the Nord Mines, you likely spotted a merchant called Gallinago the Peddler. He carries an item called an Ice Chunk. These deal 100 damage to any enemy they hit (as long as they don't reflect ice damage) and cost 270 a pop. They also deal, as you might have guessed, ice damage. However, keep in mind that single-use items like these deal a fixed amount of damage so (even though the boss is weak to ice) they'll [[link]] still only deal 100 damage.
You're going to want to buy as many of these as possible. With no mages in your party, you'll want at least 20 of them before taking on Mauna. Consider selling any treasure items in your inventory if you can't afford this many. Otherwise, just buy as many as you can. I know that sounds like a heavy investment, but don't fret—money is easy to find in Metaphor, so you'll make that back in no time. And beating Fire Dragon Mauna actually nets you 1,000, so consider it an investment.
Another tip: if you've entered the part of the map where Fire Dragon Mauna is, you might have noticed that you can no longer backtrack through the Nord Mines. Obviously this means you can't go back and talk to Gallinago the Peddler. There's a simple fix here—to backtrack, fight Fire Dragon Mauna and die. You'll be sent back to a slightly earlier spot in the Nord Mines, which means you can now backtrack freely. Don't worry, there are literally zero ramifications for dying here. You won't lose any progress, [[link]] experience or money.
To prepare for the fight, ideally include a mage in your party outfitted with Blizz, and cast it whenever possible. Use your Ice Chunks like mad. If you start to run low on MP and/or you start to run out of Ice Chunks, use your ice attacks at the start of your turns and then guard afterwards with your extra turns. Move to the back row so you take less damage. Ice Chunks will deal about half as much damage as Blizz, so without any mages this will take twice as long as the next method, but it's a slow, steady, reliable victory.
How to beat Fire Dragon Mauna the harder way: Grind the mage Archetype
Fire Dragon Mauna's weakness to ice is useful for two reasons. Firstly, ice attacks will do more damage. Standard stuff. Secondly, and more importantly, using an attack that takes advantage of an enemy's elemental weakness grants you an extra turn in combat. You only get one extra turn per party member however, which means that using three ice attacks on Fire Dragon Mauna will net you six turns in total.
By this point in the story, your bond with Gallica will have automatically improved. This will have unlocked the mage Archetype. At level two, mages unlock the Blizz skill. You should have naturally earned enough MAG by now that you can respec all three of your party members into mages.
Now comes the hard part. You'll have to farm the enemies nearby for EXP so that all three of your party members rank up to mage level 2. Once you've done so, the fight against Fire Dragon Mauna is simple: use Blizz with all three party members every turn. Depending on how you've allocated your stats up until this point, this should take roughly three to four full turns.
Remember to move your party to the back row. When a party member is in the back row, they take less damage from all forms of damage. Usually, the trade-off is that you'll deal less damage in the back [[link]] row vs. being in the front row, but this only applies to physical attacks. Ranged attacks, such as elemental spells, are not affected by this damage reduction. This includes Blizz.
This method is a pain since you have to waste time farming enemies, and you might not even have enough MP to spare and will have to use basic attacks to conserve your MP while you farm enemies, slowing the whole process down further.
Your reward for beating Fire Dragon Mauna is a bunch of EXP and A-EXP (which scales based on your level), 100 MAG, and 100 money—but that's not what we're here for. Beating this boss will grant you access to the treasure chest behind it, which contains the Dragon's Indignation Greatsword.
Trust me when I say this weapon was worth the trouble, whichever strategy you chose. It's a Warrior class weapon that has a base ATK stat of 111, which will deal way more damage than any other weapon you'll acquire for quite some time. Most importantly though, it deals innate fire damage. This will be extremely helpful during the next main quest dungeon, because most of the enemies you encounter there are weak to fire. Also, it looks cool so, y'know, style points.