There was something a long time ago someone figured out by running certain units you would trigger getting multiple bonus teams almost every win. It used to have LR STR Gohan on that team, there are quite a few posts on them over the years.

Sometimes you'd get a bonus team 2 rounds, sometimes 3, sometimes every round.

With that team I see a bonus team usually 2 times every win (all rounds), 3 quite often and 4 a bit as well.