The Final Dungeon
Your next destination is the Final Dungeon, otherwise known as the Northern Cave. Before entering it, though, you might want to explore the FF7 world and get all the secrets you've missed, such as chocobo breeding, defeating the Emerald and Ruby Weapons, and finding everyone's Limit Break manuals and ultimate weapons.
When you're all through, prepare for your
destiny within the Northern Cave. Follow the winding path and
you'll eventually come upon several diversions. Choose your
parties and take whatever path you wish to. In these paths,
you'll be able to find a Tetra Elemental, the Shield materia, the
Mega All materia, the Magic Counter materia, and the W-Magic
materia. 
The marshy area, by the way, is a great
place to build up EXP and AP. Hunt especially for Magic Pots.
Whichever path you choose, you'll eventually meet up with your other allies. Talk to them and get fro them treasure they've found. Before heading to the next area, you might want to explore the other areas to get what you've missed.
Once you're all through, head through the floating steps and you'll eventually come upon Jenova•Synthesis. The fight between this enemy boss is easy, but the upcoming fights with Sephiroth are hell.
Everyone should be buffed up by now: Strength, Defense, Magic, everything! Also, everyone should have at least level 3 Limit Breaks and Master materia, as well as many Megalixirs. Choose your party members and get ready for two extremely tough battles!
Your first battle is with Bizarro Sephiroth. Cast defense spells immediately then pummel away with W-Summon + Knights of the Round, which makes the battle extremely easy. However, don't use that if you want some challenge in this penultimate battle. Use physical attacks on the Head, then destroy the Left and Right Magics, and then give everything you have on the Core. Summon Phoenix if your allies die.
The next battle with Savior Sephiroth is
just as difficult, but it can be just as easy with W-Summon +
Knights of the Round. But as for you challenge-seekers, avoid
using that. Cast defense spells immediately and hope you have
plenty of Megalixirs available. Besides the obvious reasons for
this is that when Savior Sephiroth's HP gets low, he will cast
Super Nova, a Summon-spell that takes A LOT of HP. Good luck!
Next, Cloud finds himself hurled through a
vortex. At the end of that vortex is Sephiroth, waiting for a
mano a mano. Fortunately, you have the Omnislash Limit Break
available even though you didn't have it before. Use it to kill
off Sephiroth once and for all. Then the ending occurs...
Next Section: Final Fantasy VII Finale
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Section: Final Assault on Midgar
