We use if + past perfect to talk about an imaginary or hypothetical situation in the past. And we use would have, could have or might have + past participle in the main clause to talk about the result or consequence of that imaginary situation.

If clause (condition) 

had existed (past perfect simple or continuous )

Comma 

Main clause (the result) use would, could, might + have + past participle

Use unless instead of not 

No comma when you put the main clause at the beginning

 If you had come to class more often, you would have passed the test.

Mixed conditionals 

Past condition (3rd conditional)

If clause (condition) 

Had past perfect, simple or continuous 

Comma 

Present result (second conditional)

Main clause (result) 

Use would, could, might + infinitive 

Present condition (2conditional)

If clause 

if a condition verb in past simple or continuous

Comma 

Past result (3 conditional )  

Main clause 

The result + would, could, might + have + past participle 

I heard that she won the lottery, apparently she bought one ticket just for fun, but someone told me that she didnt believe in that things. She was like “that cant be real, no one is going to give me money for free”

Well, turns out it was real, she won 2 million dollars. You’ll never guess what happened!

What happened was that she build a house for her dogs, Popy and Taco. The funny thing was the dogs didnt wanna live their, they always sleeps on the backyard. In the end she lost all the money and had to sell the dog house and all her things and end up living under a bridge.