The enemies inside the Pyramid are fairly dangerous. If you encounter too many enemies in one room, back out and come back in for fewer enemies to fight. The Fierce Shattered Men and Petrified Guards are the most difficult, so be careful when fighting them. The heiroglyph enemies on the wall are always there until they are defeated, no matter how often you use the disappearing enemies trick. Be careful because they can give you a cold.
Head to the right and up the stairs. You'll eventually come across a casket which contains a Viper. Grab it and continue on. You'll soon see a casket sitting on a pedestal. This will be important soon. For now take the left room up some more stairs to find a Bag of Dragonite. Head back down to the right and continue down the stairs. Very soon you'll find a Speed Capsule and Cup of Lifenoodles. Go farther to the right and you'll descend a lot more stairs. The next casket blocking the door is a boss!
After the boss is defeated, head into the next room. Make sure to grab the Rain Pendant while there and then step on the switch on the bottom left side of the room. Give the Rain Pendant to Paula and have her equip it for a nice increase in defense. Head back up to the room with the casket sitting on the pedestal and you'll see that the casket has been moved, revealing a hole. Jump down the hole and you'll find the Hawk Eye. Since Poo will be leaving your party for a short amount of time pretty soon, give the item to him. It'll be placed in Escargo Express and when you need to get it back, they deliver it for free. This opens up an extra item slot in your inventory for a while.
Continue to navigate the Pyramid by heading to the right. You'll come to a room with a hole, but make sure to grab the Diamond Band from the casket first. Equip it to whoever has the lowest defense (except Poo, who can't equip it anyway). Make sure you have full HP before dropping down this hole because you may be ambushed by a lot of enemies. Now continue to the right to exit the Pyramid.