In my playthrough Bulette didn't even burrow out until I reached the Sussur tree loaction.
I'm also not sure why people are even attempting a lv5 boss without having a source of Bless in the party to actually land skills on a mob 1 level over you.
In that party comp 3 out of 4 didn't even have Darkvision.
Your playthrough is the exception and not the rule given that the Bulette can and does regularly show up near the minotaur patrol area and can show up during the battle. As to bless or being 5th level, I'm not sure how you can type that with any seriousness considering the bulette can take flying bellyflops off of high ground and do 250 damage to multiple party members.
