monster next door

[Lydish]

Overall, good work! I like the measured meter--gives it a whimsical feel that's a lot of fun. The occasional use of rhyme gives it a lyrical sound too.
I think maybe some of the images you use are a bit cheesy/overused. There's nothing necessarily wrong with it, but it does give the language a more common tone. In some places, I also thought you could condense multiple lines into one.
More is pointed out in bold below

This bright and cheerful morning

I step out of my door.

The air is warm and breezy,

it caresses my brow.

The lines in this stanza are all kinda generic. I wonder if you could either use more specific images, or just combine it into the second one?

The sky, the birds, the treetops,

demand musical applause.

I feel an urge to please them,

I like this line "an urge to please" "demand musical applause"

a whistle stirs my soul.

 

Lost in this melodic trance,

my gaze drifts lazily down.

I let it follow a languid leaf,

as it spirals to the ground.

But what is this I now behold?!

I would either use more specific wording to give the "!?" tone, or just put an exclamation mark

Surely, this is a trick!

For it simply cannot be,

that a monster sits next door.

Its hideous head is huge and red,

its body glows with hidden embers.

The sinuous tail is slowly swaying,

to a treacherous tune that speaks of death.

If my tongue wasn't suddenly dry,

and my limbs weren't suddenly frozen,

I'd have expressed my indignation

at this rude, improper intrusion.

But as it is, I am standing still,

silently watching the creature.

"silently" doesn't sound scared enough for a reaction to me, but maybe it's on purpose?

It seems to be unaware of me,

it seems absorbed in a book.

But I know better than to trust

this scheming, plotting, malicious beast.

It's waiting for my guard to drop,

and in that moment it will pounce.

All thoughts of peace have left me now,

and in their place there's heavy dread.

I dare not blink, nor breathe too hard,

I would just go with "I dare not blink. I dare not breathe." but I also think this and the "heart pounding" line are both pretty typical

I wish my heart'd stop pounding.

On a fleeting whim, I decide to run.

I'm so confused by the narrator. Runs away on a fleeting whim, but is so scared they can't blink/breathe?

Let the dragon get me if it will!

As I see it, I'm doomed anyway,

I might as well die trying.

Could refine the meter for this stanza :-)

After three endless seconds,

I've finally reached the end of the street.

I sit here crouching under a bush.

I know the monster's coming.

I have been sitting motionless,

and quite some time has passed.

Even the sun has moved in the sky,

You probably don't need a full stanza to say that time has passed

it's now right overhead.

Slowly, carefully, I rise to a stand,

and peak into my street.

The monster hasn't moved and inch,

it's still flicking through its book.