Each wave had 7 different Untu, plus the first officer and captain, made for a total of 30 Untu - one for each day of the month. Most of the Untu's had a word count close to 1,667, the number of words you'd need to write a day to write 50k words in a month (the goal of NaNoWriMo). Once the wave had passed the Untu from that wave wouldn't return again, so if you wanted to unlock all of your monsters for the Bestiary, you'd have to fight a different Untu each day.
The event ended in the first week of December with over 15,000,000 words written. The Untu returned to their home planet and would be back before anyone expected in April 2017.