Learn Spanish (Latin America): ¡Ni que el conde hubiera dormido en ese ataúd sucio! - As if the count had slept in that dirty coffin!

We use the past perfect subjunctive because the indignant reaction is about an event that supposedly already happened ('had slept'). If you were reacting to a present or ongoing situation ('As if he were sleeping in that coffin!'), you would use the imperfect subjunctive: ¡Ni que el conde durmiera en ese ataúd sucio!

What is the literal meaning of ¡ni que!, and why does it mean 'As if!'?

Literally, it translates to something like 'not even that' or 'nor that.' It is a fixed idiom used to express sarcastic disbelief or indignation, similar to 'It is not as if...' or 'As if...' in English. Because it sets up a hypothetical or rejected reality, it always requires a past-tense subjunctive.

Could I use hubiese instead of hubiera in this sentence?

Yes, hubiera dormido and hubiese dormido mean the exact same thing. In Latin America, the -ra endings (like hubiera) are much more common in everyday spoken Spanish, but hubiese is grammatically correct and widely understood.

Why is ataúd masculine (ese ataúd) when most Spanish words ending in '-d' are feminine?