Unfortunately for Muku. These beasts weren't as weak as the ladies from before. Whether in terms of strength or mental fortitude.
All of them had a tale to tell, like any strong being. For that reason, they were rather resistant to things like mental attacks unless they were overwhelming.
While Muku's [nightmare] could be overwhelming. It wasn't there yet. After all, he recently discovered it and had only used it once. So obviously it wasn't too strong yet.
For that reason, the beasts were only trapped for three seconds before most of them broke free.
As for why it was most of them and not all... Well, for beings like Muku, three seconds might as well be thirty minutes.
And what can someone accomplish in thirty minutes? Well, normal people might not be able to do something significant. But Muku was different.... He was able to take out around a thousand beasts in those three seconds.
