The Ancient Forest
Just east of Cosmo Canyon is the Ancient Forest, a place of mystery, puzzles, and a whole bunch of frogs and bugs. It's accessible at first via bred chocobos, but once you've defeated the Ultimate Weapon, it'll be accessible by foot. Getting through the puzzles of the jungle will award you with several items, including the Slash-All materia, the Typhon materia, and Cloud's Apocalypse sword with the triple growth. However, if you somehow get stuck and can't get out, just press [SWITCH] to get back to the beginning of the forest.
In the Ancient Forest, you'll encounter many bags and various wildlife. You can pick up the frogs and bugs by pressing [OK]. Put them into empty bags and you'll be able to cross. Note, however, that they won't stay in for long. Frogs will jump back out and will be "reusable" while the bugs will merely disappear. You'll also encounter plants that snap shut when you touch them, taking away a considerable amount of HP, and you'll find beehives to place into them.
In the first area, collect the bugs bouncing around and bring them into the arean near the bridge. Place them and the frog into the bags one by one then cross quickly. and head east to the next area.
Next, pick up a bug and leap to the ledge. Put the bug in the bag and leap onto that then to the second, already full bag. Pick up a frog and leap onto the right bag and place it in the other bag. Hop to the top and pick up the beehive. Jump down and place the beehive into the plant, which will subsequently shut up. Take the now-accessible Slash-All materia. Pick up the frog again and climb to the ledge. Place the frog into the right bag. Jump onto it and wait until the frog jumps out, which will send you flying to the opposite side of the snapping plant. Head east to the next area.
Grab two bugs and place them into the bags. Leap across to the pink vine, which will send you flying to the treetops. Head east across the vines to pick up the Typhon materia. Head back west across the vines and head down the branch in the middle of the area (use [ASSIST] to help you).
Back on the ground, grab a bug and head for the ledge to teh east. Hop aboard and place the frog into the bag. Hop onto it and head onto the second bag and then into the ledge with the beehive. Head back down and place the beehive into the plant. After it snaps shut, head west over the chasm and pick up a bug. Head over to the tree with a hole and a frog-like noise. Place the bug into the hole of the tree and a frog will pop out. Take the frog and head back east. Put the frog in the bag and stand on the bag and wait there until the frog leaps out, sending you flying to the east. Enter the cave and procure the Apocalypse sword in on the chests there. Head north out of the cave and out of the Ancient Forest.