He didn't dare to try this until Sith, and his team, would start their attack. And when that happened, what William waited for happened.
The tigers got into disarray the moment Sith and his team joined the fight. When William was feeling little pressure here, the tigers had to shift most of their attacks away, relieving most of the pressure away.
"Thanks," William shouted, while not hesitating anymore and flashed into the middle of a group of dead monsters that he killed before.
In the middle of all this chaos, he took the chance and started to collect the cores he missed before. He didn't try to attack a single monster this time, leaving Sith and his team to deal with the rest of the tigers while he collected his loot.
And this time, William couldn't help but laugh from time to time, happy about his gain.
"One hundred silver cores… Hahahaha! That's how it should always be, hahahaha!"