Is there something he could try to use as a  improvised oar? On a related note, is there some obvious destination on the other shore?

The boathouse itself doesn't look especially sturdy; he could probably pry a board loose. 

The far shore doesn't have a dock, but it's not too high above the water. He could clamber up from the boat and reach the postern door if he made it across. 

He'll try to paddle across with a board then. In any normal circumstance this would be a bad idea but so would going through a thorn hedge.

The board does not appear to object to this treatment.

A second after he hops in the boat, however, it begins to move forward without any input from him. 

Maybe he should have predicted that but oh well the board might still come in handy.

Halfway across the moat, a familiar voice yells, "Alex!" 

"Hello. Is it time for your game?"

By way of answer, a sopping wet sponge hits Alex in the face. Muddy moat water dribbles down his front, and the boat immediately reverses course. 

Melias cackles with glee. 

"I see, so the boat only takes me across when I'm dry and the boathouse is enchanted to dry me off. Could I get you to stop trying to make me wet somehow or do I just have to block your throws?"

As he speaks, the sponge flies back into Melias's webbed hand. 

"Play the game however you like, Alex! I am bound to trouble you, of course, and would hardly be denied my fun in any case. But a hint may be in order, if you've something interesting to offer in exchange." 

"And what sort of things do you find interesting?"

"Stories, or pieces of them. The calling card of a rebel who killed an emperor, a spearhead that slew a demon, the words that sundered a tribe, that sort of thing.

"That's practically a hint on its own, you know. I suppose you can owe me one. 

"Or you could be boring and agree to serve me for a year and a day." 

Meanwhile, the boat returns to the boathouse and Alex's clothes begin rapidly drying again.

Alex won't dignify that with a response. He doesn't have any precious artifacts like that and he's certainly not swearing to serve a fae just for getting an answer to a question. On his next attempt he'll try to see if he can block the sponge with his convenient board. Maybe it's futile effort but it would feel worse not to even try.

Melias pouts at him but doesn't interfere as Alex returns to the dock. He does call out "Alex!" and fling the sponge again. Alex's swing is dead-on, but the sponge swerves and curves around to splat Alex in the shoulder. It falls into the boat before rising again and zooming back to Melias.

The sponge isn't noticeably faster than a casually thrown rock, and if Alex elects to try a third time with this behavior in mind he'll find he can bat it away, but it does keep zooming back at him like a wet, angry bee. As long as the dripping board stays outside the plane of the boat's sides, the boat keeps going forward and not backward. 

If it seems like he can succeed he'll try at least a couple more times.

He's getting the hang of it after a couple tries, but keeping any splatter at all out of the boat for the whole journey is proving to be a challenge and occasionally he slips up and gets splatted by the sponge. He could probably bull through on sheer stubbornness with enough attempts? 

(Melias yells Alex's name before every throw. At least he seems to be having fun.) 

Is there any sort of pattern he can see? Melias did seem to suggest there was a way Alex could get him to stop but he's still not sure he's willing to pay the price for that. Actually, he does have an idea that it wouldn't hurt to try. "Melias, if I tell you a story will you let me across without sending the sponge at me?"

"A-ha, he talks after all!" replies Melias, twirling the sponge in a way that somehow manages to come off as menacing. "Can't do that, I'm afraid, faerie's honor, but nothing in my arrangement says I can't offer you hints. Has to be a good story, mind, a fresh story, a new story, the kind that tugs on the strings of Fate. The better the story, the better the clue." 

(Thanks to his lessons with Trefoil, Alex does have a decent idea of what would qualify, here. The kind of stories that Named live, and that warp their lives and experiences. Possibly one that's not quite settled into a larger pattern yet; a retelling of one of Trefoil's patterns-of-three would not suffice.)

An idea occurs to Alex... it's perhaps playing things excessively risky but he thinks it's just on the edge of safe.

"I might just have a story like that. It's not precisely a true story but it's not precisely false either. It's something that might have happened if things went differently. Does that sound appealing?"

There's a pause in the twirling while Melias considers. 

"Perhaps. Tell me this story, then, Alex, and I will share something of use to you in turn."

"On the 1st of Undindar, I woke up having had something like a dream of how that day might have gone. Here's what happened in that dream: I woke up and received a mysterious message which in effect suggested that I go to the festival early. After I finished worrying about how I got the message and talking with my grandmother about the message I decided to do as the message said..."

Alex goes on the describe meeting Lillian the first time and serving as get guide around the festival, the strange intervention of Aeschivus, and then the rather dramatic ending of the night with the woman putting everyone to sleep and waking up just before being stabbed.

Melias listens intently, eyes glittering. When the tale is done, he licks his lips. "That is a worthy story, Alex. If, perhaps, incomplete. It has the taste of a beginning to it, this...dream." Melias grins, showing interlocking rows of triangular teeth. "I keep my promises, of course. Your hint is that I am forbidden from interfering with guests using any power that belongs to me." 

That gives him an idea. Perhaps not the correct solution but an idea. On his next attempt he leaves the board behind and instead tries to catch the sponge.

This succeeds! Alex is now in possession of one (1) magic sponge. It tugs once in a feeble attempt to escape from his grasp, then falls inert. (This does still earn him a trip back to the dock to dry out.)

Melias laughs. "Excellent. Now when the school wishes to assign me to play games with new students, it will need to provide a more interesting toy. This one is yours; use it well, if you can." 

"If I'm understanding, I'm still not done. I freely offer you this sponge." He hold out the sponge over the water.