Iifa, the Ancient Tree of Life
An invisible force field will still block the way to the Iifa Tree. Ask Eiko about the force field, and she will explain that she needs to summon an Eidolon to break the seal. You will receive a 
Ruby during the sequence.
You can kill two of the monsters in this area very easily. There is a monster called a Stroper that you can kill by using a 
Soft on it.
There is another monster called a Dracozombie, which you can kill immediately by using curative items or spells on it, such as the 
Life spell, which is an instant kill. Both monsters are pictured below.
Walk straight forward into the next screen. Follow the linear pathway through the next few screens—there are no turnoff points, so continue along until you reach the platform where Mocchi the Moogle is standing. Take the opportunity to use a 
Tent and save your game.
You will also want to select the Mognet option so you can provide the letter from Mogryo to Mocchi. Continue to the end of the pathway, where you will find an elevator that will take you to the next level. Try standing on it when given the option.
Continue down the pathway into the next area. There is a hidden item sticking out on the right side of the screen (shown in the screenshot below). Have Zidane choose to “Push it” to release a chest on the platform above, which contains a 
Phoenix Down. There is another treasure chest at the bottom of this screen containing a 
Hi-Potion.
The next screen has another hidden switch on the left side of the screen. Choose “Push it” and then return to up to the previous screen. A newly revealed chest, located towards the top of the screen, will appear, containing a 
Healing Rod.
Go back down, following the pathway until you reach another treasure chest that contains a 
Lamia’s Flute. There is a partially hidden treasure chest located just to the left of that one, which contains a 
Remedy. Follow the main pathway down to the bottom once you have picked up both items.
The crew will stumble across a leaf-like platform attached to a large pillar in the center of a pit. Eiko will suggest that they all jump on, at which point they will all be carried down to the bottom.
There are a few fixed battles along the way. The first is against 3 Zombies, which is then followed by a battle against a Dracozombie. You can still use curative items on each of these enemies (the Life spell specifically) to kill them in a single hit.
Iifa Tree - Bottom
Take both sets of stairs down to the bottom pathway and pick up the hidden treasure chest at the bottom of the stairs for a free 
Elixir. On the left side of the screen, behind the wall that Vivi and Eiko are standing in front of, is another hidden treasure chest that contains a 
Brigandine.
You can equip your characters with the 
Body Temp ability before the upcoming boss battle if they have that ability to make the boss fight much easier. Explore the bottom-left side of the platform to find the Action Icon once you are ready to proceed.
Boss Battle
Level: 26
HP: 9,765
Soulcage is incredibly easy to defeat. Soulcage is an Undead-type enemy, which means that you can have one of your characters (either Dagger or Eiko) cast Life on it to kill it instantly. The difficulty lies in attempting to steal the items before the battle ends. The Brigandine is a fairly nice piece of armor, so you should steal it before ending the fight.
Soulcage is the first boss/enemy that is capable of inflicting the Heat status effect on one of your characters, which will happen every time that it uses its Mustard Bomb attack. Whenever a character is under the effects of Heat, they will instantly KO themselves if they use a command. You have to wait for the status effect to wear off. You can prevent this if you pre-equip your characters with the Body Temp ability before the fight, as suggested above.
If you hit Soulcage with a fire-based attack, it will light on fire and begin using an attack called “Fire Blades,” which deals an incredible amount of damage to your party members. Do not use fire-based attacks.
It is weak against Sleep, Slow, and Blind status effects, though, so you can have Dagger and Vivi cast those spells on it while Zidane is attempting to steal the Brigandine.
Steal:
Oak Staff (common)
Magician Cloak (uncommon)- Brigandine (rare)
Drops:
Phoenix PinionYou can find a video of the battle below:
After all the Mist disappears and a few more lines of dialogue, the team will agree to return to Madain Sari with Eiko.