虚拟语气中，什么时候用would have done，would do

都不对
应该是He
had
been
very
busy
yesterday
otherwise
he
would
have
come
to
the
party.
这句是对过去的虚拟所以主句要用过去完成时had+done,从句用过去将来完成时would+have+done
对现在的虚拟主句要用一般过去时did,从句用过去将来时would+do,如
If
I
were
you,I
would......(be动词在虚拟语气中只能用were,不能用was)

would
have
done是对过去的虚拟，would
do是对现在或将来的虚拟
第二句正确，“come
to
the
party”是过去发生的事，句子对过去虚拟，所以用would
have
done
顺带说一句，这句句子是混合虚拟语气。如果是正常的虚拟语气句，主句的时态是用过去完成时，但是主句中有明显的时间词yesterday，所以就用了一般过去时。

第二个句子正确。
would
do只是表示过去应该做某事。
would
have
done表示应该去做但是结果没有做，里面暗含后悔、遗憾之意。
例：
because
of
the
bad
weather,he
would
have
arrived
here
yeaterday.
由于坏天气，要不昨天他就该到了。
his
mother
asked
him
to
visit
his
sick
granny,
otherwise
he
would
have
finished
the
report.
他的妈妈要求他去探望生病的奶奶，否则他已经完成那篇报告了。
希望你能理解。