I used 10 training Hero’s and still will not level up pass 6 of 8 on Green Hero Hisan
Traning heroes are not the best way to raise the special skill.
You need to feed your hero a 1☆ heroes x10 per time to get 20% success rate.
If it was a 3☆ hero.
If it is 4☆ hero stick to same color 1☆/2☆ feeders to gain better success rate x10 feeders each time of fed.
5☆ heros feed em every thing will get 8/8 before 3/70.
BUT DON’T feed any hero a traning heroes before his skill is already 8/8.
Specially if it was 3/4☆.