Finding the Cave
Although, technically, you could get inside Yampi Desert Cave the moment you finished Gaia Rock and got the Sand Psynergy, you wouldn't have got much further - the first major obstacle is a teleport circle which obviously you can't get past without Teleport. Anyway, Teleport from wherever you are to Alhafra, then go to the northeastern Yampi Desert entrance from there.
Either climb down or let yourself drift off the first sand waterfall to get to the sandy area. Walk along this back to the left-most waterfall in this area, then climb up and get on it. Without falling off, use Sand to go up the waterfall to the top, and under the rocks. In the pool at the top, get out to the top-left and walk upwards to the cave entrance.
Inside the Cave
This isn't necessarily a long dungeon, it just seems to be very confusing. The chest to the right contains a Water of Life. Go up and use the teleport circle to access the main part of the caves. Go straight up. The door in front of you leads nowhere, as does the stairs to the right. Go left, and use Sand to get under the rocks. Use Burst on the pillar to blow it up so you can go through the door behind it.
The stairs straight upwards in the next room also need nowhere for the mean time, so go past them, and around to push the rolling pillar down. Push the other one to the right, then go up. Roll the pillar along and once it stops use Sand to get underneath it (you might want to set Sand as a Psynergy Shortcut, for now). In the next room, straight up leads to some Mythril Silver you can dig up with Scoop. Then, go right, hugging the bottom wall all the way around to the stairs down.
Use Sand to get around the rocks to the other side of the pillar. Use Move to move the pillar down one. You can't get back now, but there is another way around. For the mean time, head down into the next room. The chest to the left in this room contains some Dark Matter. Go down again into another new room. You will encounter a pillar-rolling puzzle in here. The image shown labels each pillar A, B, C and D, and the instructions below will tell you how to solve the puzzle to get past.
- Push B down
- Push A up
- Push B up
- Push D all the way to the right
- Use Sand to get under pillar B
- Push B down
- Use Sand to get under pillar A
- Push A down
- Use Sand in the bottom left corner to get behind C
- Push C to the right
There you go; you can now proceed to the left. Go up the ladder first. In the next room, hop across the Pound pillar and go down the ladder. Use Move to push the pillar across into its groove opening up a path to the lump moving around in the sand below. You'll find out what this is in a moment; for now, go back into the previous room, and through the bottom exit this time. Go the right and in the chest you will find some Orihalcon (more rare forgeable material!). Up the ladder, use Burst on the pillar. You can now hop across and return to the first main room of the caves.
Go left again, under the rocks using Sand, and enter the next room. The stairs that you ignored before you can now take, since you opened up the path. Assign Scoop as your other Psynergy Shortcut (remember - always keep Move as the other) and wait next to a tile where the mysterious moving lump may appear (it moves in a set pattern). When it appears next to you, quickly use Scoop to dig it out. Crystal, the Venus Djinni will appear, and will attack you. Beat it down with attack Djinni and Psynergies and it'll join your party.
Now, head up and use Pound to smash the pillar into the floor. Go past it and into the room beyond. In here, move the pillar onto the groove to open up one last path. Go back out through the bottom door, past the Pound pillar again, up the ladder and back into the previous room. Go past the rollable pillars to the door at the top of this area, as you did before. Hug the bottom wall in the next room all the way around to the stairs.
Now, the two pillars are in place, so you can use them to access another door on a previously inaccessible ledge. Before you go any further in the next area, save. You are about to fight one of the extra bosses, and he's tougher than you might think. Heal everyone up, but don't standby any Djinn - you will soon see why. Approach the guardian in front of the tablet, and you will be standing toe to toe with Valukar!
Boss Battle: Valukar
First of all, watch out for Stun Jip. This does quite a bit of damage to one character and has a relatively high chance of stunning them. Be prepared to survive without them for a few turns or cure them if you want. However, that's not the worst thing about this battle.
Valukar has the ability to use your own Djinn against you - he can use your summons! If you have any Djinn on standby when he attacks (he gets two attacks a turn) he will most likely use them. If you do this right the worst he will ever summon on you is either Megaera or Flora, and they aren't particularly damaging. If you're careless he might be able to summon something worse, like Haures, or possibly Coatlicue (you don't want to have to fight the battle from the start again, do you?). You will begin to appreciate just how much your summons hurt, although since summon damage is proportional to health, among other things, you will rarely take more than about 200 damage from one unless he uses more powerful ones like Haures and Eclipse.
Of course, if you were careful enough then your foe would never be able to summon against you. So, he has Djinn Stun, which puts the first set Djinni of every front party member on Standby. This can allow him to easily use something worse like Ulysses or Eclipse on you, so watch out. However, this may help you as much as it helps him, especially if he uses it for both his attacks. You will need to take into account, however, that you will rarely get the opportunity to summon anything powerful against him, so just stick to small summons.
Although he can use summons against you, he is also surprisingly susceptible to them himself - Venus, Jupiter, Mars and Mercury can all do upwards of 300 damage to him (Mercury nearly 500, since Valukar is weak to Mercury). Bigger summons like Haures and Eclipse can do around 2000, and he has about 12000 to begin with. Failing summons, strong Psynergies, healing cycles and normal attacks will work too.
Once Valukar falls, you can walk up and receive Daedalus! Daedalus requires 3 Venus and 4 Mars Djinni to summon. Although his initial attack doesn't appear to be too powerful, another attack a turn later will occur, doing even more damage. Now, you can Retreat from Yampi Desert Cave (this will dump you back at the entrance of Yampi Desert, conveniently).