That "lead" melodic instrument is perfect! It is so squeaky and mouse-like. Really cool way to fit the theme.
The time is doing weird stuff that I found hard to follow at first. I see you used the 'challenge of the stair', so it makes sense. Let me analyze... Is it doing... a single measure of 4/4, then a single measure of 5/4, and then two measures of 6/4? Ah, looking at your DAW, I see I was right! That's a very interesting idea for sure: you're not just walking up the stairs once, but you keep running up and up and up the stairs! It makes it a bit hard to follow since you switch so often, never allowing us to really find a time to grasp onto. And the 5/4 and 6/4 parts seem to be designed to sound like a 4/4, making the two beats of 6/4 sound more like three beats of 4/4 instead. From 1:23 onward, you switch to a constant 4/4 beat, giving us that resting place, which is nice. I do find this second half a bit less fitting, having this EDM-like "party"-kick.
Overal, really cool entry! You should be happy with the result, it all sounded very nice :D