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.