Hold on, you had a special ability for initiative on the early maps of this scenario, plus dragons.

No, it was different before. I first made this special ability when I submitted the fifth map to the contest. Later, when I started editing the previous maps, I added it to them. First in New Threat (a new, but non-functional version), then in Path of the Outcast, then in Burning Tour of Hell, and finally in Return of the Hero.

Added 1 hour 27 minutes ago

Well, it seems that when I started playing them, you had already changed the special ability.

Are you sure the special ability works? I'm fighting undead in the Dungeon (my hero is level 4), and it doesn't reduce their initiative at all (although it shows up in their status). Please check.
It works 100%. It's just that reducing initiative by 4% is almost nothing. For example, 4% of an initiative of 6 is just a tiny amount; it might not even be taken into account. Dragons at level 4 also rarely appear. But a hero at level 35 with a 35% initiative reduction (and if you add the Staff of the Underworld with mass slowing... :smile08:) and frequent summoning of dragons, about 40% of the hero's available summons... that's a different story.