I can’t get the super ability.

True luck. Perhaps the guide also implies a rain of arrows, an enchanted arrow, and a deadly shot, but I'm not sure.

Rain of Arrows unlocks Elven Luck, Deadly Shot unlocks Silent Stalker, and Enchanted Arrow unlocks Secrets of Light, which are the paths through which Elven spellcasters develop, so you need at least Skilled Avenger, Logistics, Light, and Luck, along with the corresponding skills from those lines. Without a mentor, I could get it around level 27-28, but ideally, you can get it at level 25. He_3JIou, in addition, you need to consider the starting skills of your main hero, because Ossir, for example, is given magic resistance and he naturally cannot take Elven Luck from the Luck line (unless the mentor doesn't sell it).