Her Majesty's Malice allows leiutenant to spend surges during attack to "perform a second attack action against the same target".

But what happens if Her Majesty's Malice is triggered during attack with multiple targets?

Would that additional attack target all targets of attack that triggered it?

For example Ariad leiutenant (2 act version) can perform multitarget attack, as she has Cursed Blast - "Perform an attack targeting each Cursed hero in Ariad's line of sight...".

As for frenzy, the attack granted must be a standard attack.

20 hours ago, rugal said:

As for frenzy, the attack granted must be a standard attack.

Yes, additional attack is just plain attack, not a special monster action that is an attack. That i understand.

It's "against the same target" part that i can interpret in two different ways

1. It restricts additional attack in a way that single target for additional attack must be chosen only from those that were targets of original multitarget attack.
2. It improves additional attack in a way that it will target all targets of original multitarget attack.

Which interpretation is correct?

1 is correct.

Ariad's Cursed Blast targets multiple heroes because it's a special action which happens to be an attack. The additional attack granted by Her Majesty's Malice is a standard attack action, so you can't use Cursed Blast again; only a standard attack which can only target a single target.

You choose among 1 of thoses target a valid target for the standard attack.