Skill Crystal

Ban was actually planning to ignore the kill confirmation notification until the Unknown Egg consumes the corpse of the Drainer Fox. 

Fortunately, he changed his mind and decided to check it when he felt a little annoyed seeing the pulsing '!' icon. 

[You have successfully killed a Lord Grade F-Apprentice Rank Drainer Fox! 

The tail can be harvested and sold for a decent amount of Coins.

A Lord Grade Beast Core can be harvested.

…

A Skill Crystal can be harvested!

...

]

Ban already knew that the Drainer Fox was only an F-Apprentice Rank Lord Grade Beast. He no longer felt that proud after learning of this and he now felt that it was only natural that he could kill it. After all, it was 'only' in F-Apprentice Rank and although Beast was supposed to be stronger than humans, that rule did not apply to Ban as he has a lot of Skills, and not to mention his body that would not lose if compared to Elite Grade Beast.