Melias snorts. "Clever! I indeed would not be able to throw it at you if it were properly mine." He grins. "But I don't particularly want it anymore, so I'll pass. I trust you'll find some worthy mischief to make with it. And if you do," he grins, "I do hope to hear the tale."

"We'll just have to see. If I have an opportunity I might just return to tell you about it." He carefully makes sure that the sponge is dry before putting it into his bag and making what he thinks is one last trip in the enchanted boat.

Melias bids farewell and disappears into the moat's murky depths with a splash. The boat crosses the distance this time with no further trouble, coming to a halt on the far shore where Alex can easily disembark.

The small iron door at the base of the fortress is unlocked; there's still not another soul in sight. 

Onward through the door and towards either the end or the next phase of this test.

The door creaks open. The hallway beyond contains several small metal rods set in sconces. Each one periodically launches a small volley of colored sparks, creating something resembling an ever-shifting obstacle course of multicolored sparks at various heights and angles. They don't look lethally dangerous, but they do look hot enough to cause burns.

Now he's wishing the sponge was still wet, but really it probably wouldn't stop the rods from working even if it was.

He'll study this for a little bit. Can he safely approach one of the rods close enough to touch it? Are there any patterns he can observe if he watches long enough?

As a matter of fact, there are! The rods seem to cover each other in overlapping lines of intermittent fire, but Alex notices something familiar about the angles involved. A bit of mental geometry will reveal that there's a few gaps in the pattern produced by the rods. The timing of the shots is trickier, but after a bit of counting and puzzling it occurs to Alex that the shots seem to follow a particular mathematical pattern which varies by rod. 

There's a gap next to one of the rods a few paces down the hall, reachable by stepping just so between shots, standing here for four seconds and ducking there for three...

Aha, and if he reaches that rod can he remove it from the wall?

Yep! It comes loose from the sconce pretty easily. It keeps shooting sparks every [slightly complicated formula] seconds but this is fine as long as it stays pointed away from Alex. Conveniently, this opens up a gap in the pattern next to another rod a bit farther down the corridor, and if he keeps this up Alex will find himself at the end of the hallway with a half-dozen rods. (He could also dismantle the whole thing, if for some reason he wants a whole bunch of spark shooters or a clear corridor.)

He considers it. But even if the school lets him keep them he doesn't expect he could find a use for more than a couple of them. Now that he's past the obstacle he'll try to examine one of the rods a bit more closely, is there any way at all for him to turn it off?

There doesn't seem to be! At least, not obviously. 

At the end, the corridor makes a sharp left; he can't see past it just yet. 

If he can't control them at all then he'll leave all but three of the rods behind and keep those carefully held in his hand and pointed away from himself and anything he might damage as he moves to the corner and carefully looks around the bend.

The corridor travels another few paces, then opens into a rectangular stone room, thirty paces across and maybe twenty wide. On the far side of the room, perhaps ten paces up, is a sizeable alcove with a large wooden door. There's no stairs, just sheer stone wall. The room is illuminated by a half-dozen crystals ensconced in the walls, no two the same color or height. 

On the floor — no, not on the floor, but floating about six inches above it — is something like a cross between a mattress and an enormous rectangular pillow, with a fluffy tassel sticking upright out of the middle. 

Huh, a fourth trial. Does that mean  there will be a fifth and a sixth or is he miscounting?

He will leave the rods behind at the entrance to the room facing back into the corridor and try to get onto the pillow. That seems to fit the pattern with the boat from before.

Aside from being unusually soft and squishy, the pillow supports his weight without difficulty. The tassel bobbles in the motion as though completely unaffected by the tendency of things to move down instead of other directions. The pillow doesn't leap into motion, though.

That would have been too easy.

He had to try though. With that test done he turns his attention to the multi-colored crystals in the walls. He'll pick one at randomly and see if to responds to him touching it.

There's only one crystal, green and halfway across the room, that is low enough he can jump to touch it. (All the others are nearer the high ceiling). It's cold to the touch, almost like ice, and it...maybe dims briefly when he pokes it? It's hard to tell. 

He'll try a couple more times to see if he can get a more definitive response. If not... well he does have those rods can he aim one of those to hit the crystal and see if that gives a response?

Nothing more definitive, no.

Attempting to naiively aim a spark-rod at a crystal from the entryway results in...the spark vanishing before it gets there, actually. One moment it's zooming happily along, ten paces above the floor, then, at what Alex knows is less than the actual range of a spark-rod, it's gone. 

Now that's interesting. He'll try getting closer to see if the burst always disappears at the same distance from the crystal.

Nope! After a few tries from a few different angles, Alex may notice that when the sparks wink out, it's always in a spot that aligns with a crystal; for instance, there's a blue crystal on the right wall eight paces into the room, and several sparks vanish eight paces from the entryway. (One or two get past, though, and vanish twelve paces in; there's a yellow crystal on the left wall twelve paces in.) 

What about the green crystal that's lowest to the ground can he get a spark to hit that if he aims at it from relatively close?

Yep! He needs to come at it from an angle, either a few paces closer to the entryway side of the room or the alcove side than the crystal. It goes dim for several seconds after it's been struck by a spark, then gets bright again. 

...around this time is when Alex notices also that the rod he's currently holding is shooting sparks approximately the same color blue as one of the farther crystals.

... do other rods shoot sparks of colors matching the other crystals? If so he'll backtrack to retrieve one that matches the green crystal and see if that has a different effect.

The six rods he removed from their sconces to create a safe path turn out to be six different colors, and the same six colors as the six crystals. When the green crystal is struck by rods from the green spark, it...turns out that the green crystal gets bright again just a moment after the green rod fires off another spark! If Alex keeps the green rod pointed at the green crystal, the green crystal will get hit by sparks at exactly the rate required to keep it from getting bright again.