Universal Communication skill

Lucas had no other way to practice his combat skills. And finding creatures to practice on could be meant that he was going hunting and it wasn't really efficient. 

For starters, he would have to first find them and then fight to practice but things didn't really go to a person's normal ways.

If a creature like the Basilon comes to attack him, then it would be tough to just practice on it as the motive of survival would be the top most priority.

That was the reason why Lucas went and took all the close-range fighters into some friendly fights. They all thought it would just be some normal fights but day by day, it became very serious. 

With the presence of a healer, it was easy to get healed no matter how severe the injury was.