Mirror

[dukealien]

Mirror

post-sinking sun,  punctuation is difficult here, see below
i’ll be in the mirror’s view. nice concept - the mirror sees as well as reflects
stripping myself of a scratchy linen, if the mass (next line) is part of you, comma could be eliminated
obscuring a writhing bedbug-mass.  these two lines are a bit difficult

unpolished and unwinding,
a statue wound of string, good showing, these two lines!
and what does its untying leave behind? is "behind" needed?

little but a ghost,
a rainbow spectre,
sculpted from merest blankness. might consider merely "mere" here 

a flow of reflective quicksilver-skin,
edifice of a million portraits.  a grand conceit here!  other people's faces reflected in the mirror skin!  Like it!
i am a shapeshifters visage, truly. good line (though there should be an apostrophe - "shapeshifter's"), especially the little "all Cretans are liars" twist with "truly" at the end

allow me be painted in your desires,  perhaps remove "be" or add "to" before it?
more likely your irritation,
you’ll soon forget me either way,
but i still hope i’ll linger in your heart. good alliteration and (I think) an original way of saying this

this plummet is a more graceful kind of topple,
dancing down the cliffside edge,
and i have decades yet to fall. very nice

exhausting, all of it,
and here still i am,
in spite. very effective
It tastes like salt.

my blood soon will freeze in my veins,
it’s burned too hot,
thought too long, blood thoughts - good!
and the echo in my reflection tires of this waltzing lie.  "waltzing lie" another good one
there are worse ways to die, cliche warning, but OK this once
but this isn’t the best.

maybe i’ll leave this place one day,
find myself ‘neath the sun’s heat,
‘neath appraising burns of azure-eyed gazes, one of those "neath" needs to be something else, I suggest
unwrapped and unmasked,
taste air touched by a first,
blue sky. perhaps turquoise, or even "azure" again to match those eyes, to escape cliche

maybe i won’t,
and maybe i’ll live off coffee,
stale oxygen,
and replace the sun with a fluorescent lightbulb.  I itch to see just "bulb" here, but that's just me.

maybe i’ll leave this earth one day,
shoot higher,
comet-high,
a planet circling round a brighter sun, should be 'round with apostrophe
and i’ll be naked in the empty,
and i’ll be loud in the quiet. perhaps simply "and loud in the quiet?"

maybe i’ll get there one day,
my tomorrow running away,
and i’ll catch it like fireflies through the holes in my net,
like fish slippery as butter leaped from my fingers,  perhaps "leaping," maybe not
like the moon chases the sun and the sun chases the moon.  could perhaps have greater impact if simplified (I won't rewrite it!)

post emancipations dream, should probably be emancipation's
i’ll cradle it close,
let it be mine for a moment,
and i’ll keep it in my ribcage,
let it warm my heart,
wrap it up in linen and say,
‘i’ll let you out one day’.

In basic critique I haven't noted all possible suggestions (though maybe too many anyway).  On that first line, it needs to grab the reader but it's difficult to read.  What you mean is "after (the) sinking sun" but also "sun after it sinks."  Though it bars the second meaning somewhat, I suggest 

post sinking-sun,

to keep the reader from halting there to try and figure it out.

The bedbug-mass is striking, but also somewhat distracting (in my opinion).  It conveys contempt for (presently embodied) self well, as a launching point for the flight at the end, but, again, you may not want the reader to stop there and react to it.

On the whole, I think this is darned good.  Don't take the multiple notes and suggestions above too much to heart; probably the firmest are those regarding grammar (apostrophes).  There's no reason to follow exact formal grammar in a poem, but going against it should have a purpose.  If you've got one, do as you like!