According to information gathered from the official forums, pets had a chance to trigger a special event known as Pet Growth upon reaching Levels 30, 50, or 80. When it occurred, the pet's base attributes would increase dramatically, and its abilities would undergo noticeable enhancement.
The opportunity, however, was extremely rare.
At Level 30, the base probability was only ten percent. The chance rose slightly to fifteen percent at Level 50, increased again to thirty percent at Level 80, and finally capped at forty percent once a pet reached Level 100.
In other words, experiencing Pet Growth at early stages like Level 30 or 50 was considered extraordinary luck, the equivalent of receiving a massive blessing from the system itself.
Several factors influenced whether growth would occur.
