The form of a dwarf is an odd one to take, at least compared to an elf. The structure is different. It's heavier, sturdier, and the chemistry more... well, more a lot of things, and less a lot of other things, but the adjective this Maia thinks he'll use to describe it is more earthy. More practical. He can see Aulë's markings all over the form; straightforward engineering solutions and economic organization in equal measure, with dashes of occasional sheer brilliance that Eru himself might be impressed by. It's beautiful and elegant in a ruthlessly efficient sort of way, which really, he can respect. Not want to emulate, were he to lose leave of his senses and suddenly decide to attempt to build a species, but he can respect and admire it.
That being said, he thinks he prefers the elven form. Not exclusively, too long spent in a single form and something starts itching at the back of his mind, but he thinks he likes it more than the dwarves. The design has Eru all over it, all expertly crafted and beautiful functions and layers and layers of perfect intricacy pulled into utterly bizarre directions. Like a master painter picked up a brush and painted a gorgeous, glittering vista, but with the perspective drawn at just enough of a skew to grate on the nerves of the viewer, even as they admired the craftsmanship. Maddening.
So of course he prefers it to the dwarven form.
The dwarves themselves were like their biochemistry; efficient, straightforward, practical. He could respect it, certainly, but it made wandering their streets unchecked a bit tricky. Also a bit boring, once he'd figured out the trick of it. Dwarves were many admirable things, and he'd be the last (well, second to last; after Aulë himself) to name them anything but a fine species, but they were so - so themselves. He'd never wish for them to be anything but, it clearly worked beautifully for them. Even so, after a while one gets very bored of bartering mutually beneficial trade agreements, properly worded contracts, and sound investments. There's only so much a Maia can poke at for personal amusement.
He's run out of options, he thinks. As delightful as their reaction to the singing mushrooms was, he can guess what would happen to anything else he threw their way. There's only so much sensible cataloging and pricing in tonal sets of singing mushrooms that he can stand, before he starts to feel less like the playful trickster deity and more like the slightly bizarre business venture deity. He adds another set of singing mushrooms in very marketable colors and tones in a nearby side cave, as a sort of acknowledgement of their skill in besting him, and then he takes his leave.
In the form of a local species of hawk, he soars above the continent, and wonders what he'll do next.