You unlock this stage by finding all 18 Sun Stones available in the standard stages in Endless Explosions.
From the entrance, drop down through the ledge to land in a cradle. Tilt the handheld right to slide the cradle in that direction, over a layer of lava. Now you'll find a switch you can trip. It causes blocks to form to the right. They linger only briefly, and there's not much reason to stand on them. You're safer floating through this area, avoiding enemies and watching out for lava rocks that will rain down on you.
Soon you'll reach another cradle to ride. Let it carry you right until a short distance before it plunges into the lava. Then you can float to the right, past more of the moving blocks. There's a weak wall to the upper left, but it only hides a red star. Keep working your way right from there until you come to another cradle, which is once again good for only a short ride. To the right, you can hit a bomb block to reveal a doorway. You can also float down and destroy a weak wall for a Keychain, if you like. Then enter the door.
Now you are in an area where the floating tanks of water hang suspended between floors and ceilings covered in lava. Work your way right here, avoiding shots from cannons, until you reach a 3D Warpstar that carries you into the backdrop. Then head right again, dodging cannon shots as you descend in that direction and finally reach yet another 3D Warpstar. Ride it again and continue swimming right past more cannons and fish until you reach a glowing doorway, which you should enter.
In this new area, there's a magic pen on a ledge overhead, and an enemy running back and forth below you. He holds a key, so you know this is a puzzle. You can jump onto the ledge and grab the pen, then jump straight up to hit a bomb block. Then you should work your way right, hitting more bomb blocks and producing pathways for your friend with the key to run across. In the backdrop, where you are positioned, watch out for volcano eruptions and falling lava rocks. You can break some rocks that fall in the foreground using the pen, which is necessary. Just watch for shadows to know that a lava rock poses a threat. If you provide a safe path far enough to the right and ride the 3D Warpstar into the foreground, your friend with the key will allow you to enter a gate along the right side of the area and collect a Keychain and some stars. It's not the end of the world if you miss it.
Hop up and ride the 3D Warpstar into the background for another chase sequence, which works in much the same way as the chase you just finished. Be careful not to get too far ahead of your friend, since you do need to protect him as he runs. Near the far right side of the area, you'll have to hit four switches to assemble a bridge, which can take some time. It's not a bad idea to race ahead once you see and eliminate the enemy sitting on a block in the foreground. If he reaches the far right side of the area in one piece, your temporary ally will open it and allow you to reach a secret doorway. Absorb the Archer enemy and enter the door.
Through that doorway, you'll find a puzzle that must be solved using the Archer ability you just snagged. You have to shoot arrows through shafts, after tilting your handheld to line the shaft up in the direction of floating targets. You should be familiar with the process by now. There are target sets in the foreground. Destroy those and you can reach a 3D Warpstar and ride that into the background. Take out more targets and enemies here and you'll reveal a Sun Stone. Grab it, then exit back into the main corridor where you protected the two enemies carrying keys. Enter the door on the overhead ledge.
You'll now find yourself fleeing from a wall of spikes. Run right to a teleportation box. Then run right again in the backdrop, grabbing and using a key to pass through a gate and reach another of the boxes. As you appear in the foreground, run right yet again and avoid spiders as you advance. You have to drop through a ledge and grab a key, then hop back up and keep moving right to pass through a gate and use another box. Then it's time to head right yet again, picking up the Beetle ability as you go and using it to destroy bomb blocks so you can advance. Keep going until you reach another of the portal boxes and you'll warp into the foreground. Then you should go right again, jumping over enemies as you go. There's another key overhead, so grab it and pass through a gate. Ahead, you'll see another box with stars in the air overhead. Quickly fly up to collect the stars, and at the top of that area you'll find the Rare Keychain: Yin-Yarn. Snag it, then drop back down and pass through the next portal box. Finally, grab another key and hop around some spiked orb enemies as you work your way up some ledges to the right. Pass through another gate, then stand on the weak blocks to the right and let them crumble. If you moved fast enough, you'll be able to drop down a shaft and enter a doorway, just ahead of the encroaching wall.
You are now in a chamber with one of the walls that comes up and tries to flatten you from the background. There is a spear-wielding enemy positioned halfway through that area, and you need to absorb him so that you can use the Spear ability to hit a bomb block to the right and clear a passage. Do so, then keep advancing from that passageway to reach safety. As you continue right from there, you'll need to hit more switches, while avoiding a continuing procession of walls. Stars and enemies are positioned along the way, and you can use their positions to know where you can safely stand as the wall passes back around. When you reach the far side of the area, you can float up and pass through a glowing doorway.
In the new area, head left along the ledges, warping between magical portal boxes. You'll head left along one ledge, past a Waddle Dee that throws an Assist Star, and then past some capsules containing the Bell and Ice abilities. Then it's time for a mini-boss battle.
NEXT: Royal Road - Stage 1
