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When you begin Earthbound, you're told by a talking bee that it's up to you to save the world from a powerful cosmic being known as Giygas. To accomplish this monumental task, you need to absorb the power of special areas known as Your Sanctuary locations. Of course, since this is an RPG, various tough bosses will be standing in front of these spots to prevent you from accessing them.
If Ness and his friends are going to save the world, they need to get to these locations. So to help you destroy Giygas once and for all, this guide will help you take down all eight of the Sanctuary Guardians standing in your way.
Titanic Ant
The first Sanctuary Guardian is the Titanic Ant, which guards Giant Step in your hometown of Onett. This encounter can be tough since you'll be fighting it all on your own. When you begin the battle, the Titanic Ant will be accompanied by two Black Antoids. They're not difficult to deal with, but they can be a nuisance as they can cast Lifeup α to heal the Titanic Ant and can call for additional Antoids to join the fray. It's best to start this fight by hitting everyone with a PSI Rockin α - or whatever you called it - attack to clear them out of there.
The Titanic Ant's main source of damage is a biting attack. This can occasionally result in a critical hit that will pretty much end the fight. It can also cast Defense Down α, Shield α, and PSI Magnet α. Since it can use PSI Magnet α and drain your PP, it's best if you use all of it on PSI Rockin α attacks. There's a good chance that the Titanic Ant will cast Shield α and cut all of your physical attack damage in half, so PSI attacks will be handy here. The Titanic Ant is somewhat susceptible to Hynopsis α, but for the most part, you can just whack it with PSI Rockin and physical attacks.
You should also stop by one of the stores in town to stock up on food such as hamburgers before you enter this fight. You're likely going to take a lot of damage, and you'll need healing items for when you run out of PP and can't cast Lifeup on yourself.
Mondo Mole
Mondo Mole can be encountered in a cave in Happy Happy Village, and is standing between you and Lilliput Steps. Despite being the second Sanctuary Guardian, Mondo Mole can prove to be one of the more difficult boss fights in Earthbound. This is mainly because when you face it, you'll likely have just met Paula and added her to your party. She'll be at level one, which means you'll need to fight some enemies to level her up to a point where she can survive this boss battle. You can get her up to speed by walking around the cave and taking on the various moles, bats, and bears that inhabit it. You can also take advantage of the house in Happy Happy Village that lets you sleep there for free to regain your HP and PP.
While Mondo Mole knows a few psychic moves like Offense Up α, Lifeup α, and PSI Shield α, it'll mainly attack you with its claws. If you see attacks that say it's about to "claw you with its sharp nails" or tear into you, there's a good chance that whoever is being hit is about to die (especially if the target is Paula.)
Luckily, this boss is very weak to Paralysis α. Ness should paralyze it right at the start of the fight as it'll make this significantly easier. Then have Ness hit it with physical attacks and PSI Rockin β - which you should have at this point - while Paula uses PSI Fire α. If Mondo Mole uses PSI Shield α, switch to physical attacks only as all of your PSI attacks will be blocked by its shield. Try your best to have Paula alive at the end of this fight since she can benefit from the extra experience points.
Trillionage Sprout
The third Sanctuary Guardian will be encountered shortly after you make your way through the secret base behind Grapefruit Falls and defeat Master Belch. Make sure to bathe in the hot springs in Saturn Valley, recover any lost HP and PP, and then stock up on any supplies you need.
Like the Titanic Ant, the Trillionage Sprout will be accompanied by two extra enemies, which in this case will be two Tough Mobile Sprouts. Use Paula's PSI Fire β to wipe them out and damage the boss. As for his attacks, he can use PSI Flash α, PSI Shield α, Paralysis α, and can smack you with physical attacks. If you see an attack that states that it "glares at you with its eerie eyes," there's a strong chance that this may diamondize one of your party members, which is practically the same as being knocked unconscious. Have a Horn Of Life or Cup Of Lifenoodles ready in case that happens. If anyone in your party is said to be "feeling strange" as a result of PSI Flash α, it's best to just put them on defense as they could end up doing damage to another party member.
This will be the first Sanctuary Guardian fight with Jeff in your party, and it's wise to make sure he always has Bottle Rockets in his inventory. Paula's PSI Fire attacks will be extremely effective in this battle as will Jeff's bottle rockets. Have Ness heal, cure status effects, and use physical attacks. Beat this plant, and you'll be able to visit Milky Well.
Shrooom!
Oddly enough, you'll find this boss before Trillionage Sprout during the part of the game where you guide Jeff through Winters to Dr. Andonuts' lab. You won't able to fight it though as you need Ness to be present for these Sanctuary Guardian battles. It'll actually be a while until you do face it as this encounter happens after you've rescued Paula from Geldegarde Monotoli in Fourside.
The hilariously named Shrooom! is actually not too tough, but his main attack is to scatter spores that will mushroomize your party. Having a mushroom on your head is one of the more annoying status ailments since it can only be cured by visiting a healer, bathing in hot springs, or entering a Your Sanctuary location (which is thankfully right behind this boss.) Mushroomization has the same effect in battle as feeling strange, which means that anyone afflicted by it may end up hitting their own teammates with their attacks. In addition to this, Shrooom! knows Lifeup α, can use physical attacks, and is able to disrupt the senses of a party member making them unable to use psychic attacks.
Much like Trillionage Sprout, the best attacks to take Shrooom! out are Paula's PSI Fire and Jeff's Bottle Rockets (you should be able to buy Big Bottle Rockets at this point, which are even deadlier.) If anyone gets a mushroom, put them on defense so they don't hurt anyone. Stomp this mushroom and record the melody of Rainy Circle.
The Plague Rat Of Doom
Getting to the fifth and sixth Your Sanctuary locations is kind of a weird trip. You first need to go all the way to Summers and then come back to Fourside after you take a call from Mr. Spoon - a curator at the Fourside Museum - while at the Summers Museum. Then you need to give him a signed banana peel from his favorite singer at the Topolla Theater, and he'll let you enter a hole leading into the sewers of Fourside. That all definitely sounds weird, but by this point, you should be used to the bizarre stuff that Earthbound throws at you.
The Plague Rat Of Doom is all about physical attacks. There's a very good chance that some of them will be critical hits, so have Ness or Poo ready to heal. One of its moves will have it bite you with poisonous fangs. Poison is pretty easily treated with Healing β or a Refreshing Herb, so it's not too bad.
In fact, the Plague Rat Of Doom is pretty easy for a boss as you can demolish it with Jeff's Big Bottle Rockets, and your strongest PSI Freeze attacks from Paula and Poo. After this battle is won, you'll climb up the ladder to get to Magnet Hill, which is apparently just sitting behind a wall in Fourside. Make sure you pick up the Carrot Key inside the gift box that's sitting here as you'll need that to get to the sixth your Sanctuary location, Pink Cloud.
Thunder And Storm
Pink Cloud is guarded by a pair of ghostly creatures known as Thunder And Storm, although they attack as one enemy instead of two. As you may suspect by their names, the duo uses thunder attacks, so be sure to have the Franklin Badge in someone's inventory. They also have a move where they "intertwine" with a party member, which can do massive damage.
However, these guys can be bested in the same manner as the Plague Rat Of Doom. Use Big Bottle Rockets and PSI Freeze attacks, and you should be able to see Pink Cloud in no time.
Electro Specter
The difficulty of the last two Sanctuary Guardians will largely depend on if you went hunting for Poo's weapon, the Sword Of Kings, and how well that hunt went. If you decided to not grind out battles for the sword, or you somehow got it very quickly, then these battles will be reasonably tough. However, if you're like me, and somehow hit level 80 while trying to get this dang weapon, then the rest of the game is pretty much a cakewalk.
The Electro Specter is guarding Lumine Hall, which is reached by going through a hole in Tenda Village after giving them the Overcoming Shyness book. This boss uses a lot of the same devices as Jeff such as the Neutralizer, Hungry HP-Sucker, and Shield Killer. It also uses a lot of electrical attacks, so keep that Franklin Badge in your inventory to deflect them. This boss also begins the battle with PSI Shield β, so don't use PSI attacks until you use Jeff's Shield Killer or Neutralizer to get rid of it.
At this point in the game, you should be able to buy Multi Bottle Rockets for Jeff, which can do a ton of damage. These projectiles are a bit expensive, but you should have plenty of money in your bank account from your dear old dad. If Jeff has a bunch of Multi Bottle Rockets, you should just have to fire those at the Electro Specter to end this battle. If for some reason you don't have any of those, be sure to get rid of this thing's PSI Shield, and then wallop them with powerful PSI attacks like PSI Freeze and PSI Rockin.
Carbon Dog/Diamond Dog
The final Sanctuary Guardian is one of the few bosses in Earthbound that has more than one form. After traversing the dinosaur-ridden land of the Lost Underworld, you'll enter the cave that leads to Fire Spring where you'll run into the Carbon Dog. Since this creature is a dog made of fire, it shouldn't be surprising to learn that it has powerful fire attacks that can potentially take out your whole party. It'll either "spew out a flaming fireball" at one party member, or "shoot out a spray of fire" which is the equivalent of using PSI Fire Ω on the whole team. It'll also use biting attacks.
PSI Freeze attacks are a good way to take it down. Have Paula and Poo hit it with their strongest forms of PSI Freeze while Ness heals and Jeff uses physical attacks. After you've done enough damage, this boss battle will enter its second phase as Carbon Dog will become Diamond Dog.
It'd be wise to hold off on using Jeff's Multi Bottle Rockets until the second part of this boss battle. Once Carbon Dog transforms into Diamond Dog, it'll immediately have Shield β active, which deflects physical attack damage back at you. That means that this shield will send Bottle Rocket attacks back at Jeff and probably kill him right away. When Diamond Dog appears, use Jeff's Shield Killer or Neutralizer to get rid of its shield.
Diamond Dog uses a lot of biting attacks, including one where it'll bite you hard which may diamondize a party member. It may also "emit a glorious light," which can inflict all sorts of status effects like paralysis, uncontrollable crying, feeling strange, or being knocked unconscious. Take down its shield and then hammer it with Multi Bottle Rockets.
Diamond Dog can be pretty tanky, so beating him without Multi Bottle Rockets will take a while. If worse comes to worst, teleport to the nearest merchant that sells them and stock up. Should only take a few of them, and then you can access the final Your Sanctuary location, which is when things start to get really weird. And that's saying something when it comes to Earthbound.