Not quite at the end, I think, but here's a start. Notice that

the first letters of each line of the riddle spell out "NO LAST FIRST".

If you interpret that to refer to

the last word of each line:

mice of glows mint she's bound when ace if worth misbecoming

and the

first letter of each of those words, I think NO LAST FIRST means that we should drop the first letter from each of those words. This leaves:

ice f lows int he's ound hen ce f orth isbecoming

And that can be rearranged into

ice flows in the sound henceforth is becoming

Which I'm sure is not the end, but seems like the next part of the riddle.

Not quite at the end, I think, but here's a start. Notice that

the first letters of each line of the riddle spell out "NO LAST FIRST".

If you interpret that to refer to

the last word of each line:

mice of glows mint she's bound when ace if worth misbecoming

and the

first letter of each of those words, I think NO LAST FIRST means that we should drop the first letter from each of those words. This leaves:

ice f lows int he's ound hen ce f orth isbecoming

And that can be rearranged into

ice flows in the sound henceforth is becoming

Thanks to @Sid, the answer to this is simply

Water, because if ice is flowing, it is henceforth becoming...water!