Scripts

It's possible, but it's not that simple anymore. In short:
- We disable the weekly spawn days for creatures;
- We add objects from the entire map to an array, with our conditions (in this case, all creatures of the same race);
- After each battle, we create a new array for the entire map, and if there are no creatures of a certain type left, we mark the task as completed.

Although the algorithm is very simple, implementing the above is not that easy. It's not a given that it will work.
Of course, there might be an easier way, but this is what came to my mind for scripts.

a few minutes later...

Here's a simpler option :), but it's more cumbersome and not universal:
Pre-place all non-random monsters on the map, disable the weekly monster spawn, give monsters of a certain race names, after each battle, check if each object exists on the map, and if none are left, the condition is met.