The mixed conditional describes a hypothetical present result of an unreal past condition.

Conditionals are all about time.

2nd is in the present but uses the past to tell us it is hypothetical.
Condition – If I were younger, (present)
Result – I would look prettier (present).

3rd conditional is in the past and is again hypothetical.
Condition – If I had studied Medicine, (past)
Result – I would have been a Doctor. (past)

In mixed conditionals you can use any part of the conditional (condition/result) depending on when and what you are trying to say.

Example.

If I had studied Medicine, (3rd condition past) I would be a Doctor now (2nd result present).
If Raul we’re not so ugly, (2nd condition present) I would have married him (3rd result past).

Grammar
Structure of Mixed Third/ Second Conditional
In this type of mixed conditional sentence, the tense in the ‘if‘ clause is the past perfect, and the tense in the main clause is the present conditional.

If + Past Perfect, Present Conditional (would/wouldn’t + Verb (bare form))

For example:
If I had listened to your advice, I wouldn’t be in the mess. (but I didn’t and I am)
If he had checked the map, he wouldn’t be lost. (but he didn’t and he is lost now)
If I had gone to university, I would be a doctor now. (but I didn’t and now I clean hotels)

Using the Mixed Third/ Second Conditional
We use the mixed third/ second conditional to express that if something had been different in the past there would be a present result.

For example:
If you had taken my advice, you wouldn’t be so unhappy now. (but you didn’t and you are still married to that horrible, lying, cheating evil bitch)

Mixed Second/ Third Conditional
The mixed conditional describes a hypothetical past result of an unreal present or continuing condition.

Structure of Mixed Second/ Third Conditional
In this second type of mixed conditional sentence, the tense in the ‘if‘ clause is the simple past, and the tense in the main clause is the perfect conditional.

If + Past Simple, Perfect Conditional (would/wouldn’t + have + Past Participle.

For example:
If I were a good cook, I would have invited them to dinner. (but I’m not and I didn’t)
If you weren’t such a poor dancer, you would have got a job in the chorus line in that musical. (but you are and you didn’t get the job)

Using the Mixed Second/ Third Conditional
We use the mixed second/ third conditional to express that due to certain present conditions something already happened in the past.

For example:
If you were a better cook, that meal would have been edible! (but you’re not and it was horrible)

Note
In these mixed conditional sentences, you can also use modals in the main clause instead of would to express the degree of certainty, permission, or a recommendation about the outcome.

For example:
If he had enough money, he could have done this trip to Hawaii.
If he’d gone to university, he might have a better job.