When I am reading slush there are a few words which indicate I may be dealing with a novice.  Admittedly, this may be my own misconception but I tend to see a correlation between the quality of the writing and the use of the list of words below:

Obsidian

This is often used as a material for a weapon, like sword of knife and particularly a magical weapon.  I believe the black glassy nature of the material stirs up darkly romantic notions about it in the author’s mind. In reality it is a terrible material to use for a weapon and almost impossible to mold.

The other use of this word tends to be a fancy synonym for “black”, or at best “shiny black”.

Suggested alternative: Black

Klaxon

I think it is the X sound that gives this word an allure.  It’s got a near onomatopoetic quality to it and even sounds kind of alien. I get why someone would be attracted to this word but to me it gets overused and often feels forced.

Suggested alternatives: Alarm, Horn, Buzzer, warning

Crimson

Often used to describe blood. In my opinion crimson is usually slightly off from the color of blood – not that I see a lot of blood, I actually try to avoid it.  Google the word and there tends to be a continuum of hues that constitute what could be called crimson.

Suggested alternatives: Red, Maroon

I suspect people want to use words that sound cool, to make their writing sound like good writing, but the use of these words tend to have the opposite effect on me.

Iridescent

This one is more of a maybe. It can be the best word to use for the situation, but I also often see it forced into prose to flower it up. I will also see it used where I think the author wants to indicate shimmering, which isn’t exactly correct.

Suggested alternative: Pearly, color-changing, or shimmering if that is what is intended.