The party explores the Cave of the Past in EarthBound - or the present version of it, anyway.
EarthBound owned by Nintendo.
Images used for educational purposes only.

Preparations

The time of truth is at hand. There’s only one dungeon between yourself and Giygas now, and it’s a doozy. Not long, necessarily, but the Cave of the Past is populated by the most powerful monsters in the game. Moving through this dungeon is no picnic.

Yet monsters are not the worst part of this place. The Cave of the Past is, in essence, a one-way trip. Once you’re there you cannot go anywhere else in EarthBound until you defeated the final boss. Consequently, you should not step into the Phase Distorter in Saturn Valley without some preparation.
  • Collect any final items you think you may need before you set out. This includes equipment you may have missed and restorative items, such as Horns of Life or Magic Truffles / Puddings. Don’t worry about saving money anymore.
  • Set your inventories up to be exactly as you’d like. You will not have access to Escargo Express or its stores once you enter the Cave of the Past. Get rid of any items that have outlived their usefulness (the Erasers, any Keys, Postcards, nonsense like that) and fill your inventories with stuff that will restore your stats alone. 
  • There’s only one item to be found in the Cave of the Past besides stuff enemies may drop, so don’t enter the dungeon with half-full inventories.
  • If you think your level is too low, build up your experience for a while. The Fobbies of Lumine Hall are good for quick grinding. You can fight in Onett if you really want, but it’s a dangerous idea.
  • Pick up Night Pendants to guard against Flash attacks. Earth Pendants are good too, but Night Pendants will save you against some of the final boss’s most deadly attacks.

The party, roboticized, arrives at the Cave of the Past in EarthBound.

Cave of the Past

- Pop into the Phase Distorter once you’re done with the world. (A spare save outside the Cave ain’t a bad idea.) Poo will learn Starstorm Omega after a cut scene, and you can find a Horn of Life by checking the destroyed Phase Distorter on the right. Talk to Dr. Andonuts to jump to the final dungeon.

- Upon arrival you’ll have access to the Phase Distorter, which can completely heal your team and provide telephone services, though only to save. As mentioned, the Cave of the Past is home to some nasty enemies, along with those nasty Ghosts of Starmen:
  • Squatter Demons hit hard and like to poison and diamondize your guys. Fire works fairly well.
  • Ultimate Octobots still aren’t too bad, like their kin, though their propensity for stealing items makes them annoying adversaries in this limited dungeon.
  • Wild ’n Wooly Shamblers are protected against psychic attacks. Physical strikes are the order of the day.
  • Nuclear Reactor Robots like to heal their teammates, and are quite annoying. Beat them last, though, as they will blow up and inflict a buttload of damage to your party.
  • Final Starmen reflect PSI attacks, use insanely powerful attacks of their own (Starstorm!), and can revive defeated members of their party. OW. These things have to die first.
  • Bionic Krakens are basically stronger versions of normal Krakens. Powerful, but honestly not that bad compared to a lot of other enemies here. Bionic Krakens have a one in 128 chance of dropping a Gutsy Bat, Ness’s best weapon. This can take so long that it’s really not worth all the effort required.

- The path to Giygas is as simple as can be, and aside from one initial branch that leads nowhere your walk is self-guided. You’ll find a Legendary Bat, sitting in plain sight, along the way. Use the big, silver orbs to teleport, and eventually…

- … you’ll find a cave…

- … and in the cave…

The party battles Pokey and Giygas, the final bosses of EarthBound.

Giygas and Heavily Armed Pokey

It begins, and, yes, Pokey’s part of the final battle. Does this surprise you, really? Though there are two targets in this battle, there’s no point in attacking Giygas now. Your attacks will do worse than nothing. Focus all your firepower on Pokey, especially if you have any Bottle Rockets. PSI Freeze is another good attack, though try to preserve Poo’s PP by letting Paula do most of the hitting. Giygas will typically use PSI Rockin while Pokey attacks physically or lowers your offence, and while both of them are dangerous, this part of the battle probably won’t last long enough for any of your characters to get killed.

The party battles Giygas, the final foe of EarthBound.

Inflict enough damage on Pokey and he’ll leave you to deal with Giygas solo. The battle now changes, and Giygas begins using a series of attacks that have no discernible form, but which heavily resemble PSI Flash. One minute you’ll be crying, the next you’ll get knocked out in a single hit, regardless of HP count. Guarding against Flash will make this part of the battle much easier, as Giygas’s attacks which do HP damage are fairly few and far between. Keep using the same tactics on the monster and, eventually…

Giygas, archenemy of EarthBound, begins to break down.

… the final phase begins, after Pokey pops in for one more chat. Giygas’s methods don’t change, but yours must, as his health is absolutely titanic. The only way to really get through this part is to use Paula’s long-ignored command, Pray, nine times. Each time you do you’ll trigger a cut scene, and the more you do, the more unstable Giygas becomes. Your only objective here is to keep Paula alive, and preferably one of your healers. Don’t attack, just heal and Defend while Paula does her thing. Even if it doesn’t look like it’s working anymore, keep Praying. Succeed and you’ll bring Giygas down.

The party collapses outside Giygas's cave in EarthBound.

Beating Giygas will, obviously, bring EarthBound to an end. Yay! You win! After a lengthy extro you’ll be free to roam the world as Ness and Paula, and most everyone will have something new to say to you. It’s a fun journey in itself, and when you get Ness back home… well, you’ll see.