Whenever another permanent enters the battlefield under your control with one or more +1/+1 counters on it, Botanical Brawler's last ability will trigger.

For each other permanent you control, Botanical Brawler will count +1/+1 counters having been put on that permanent at any time during that turn, even if Botanical Brawler wasn't on the battlefield at that time. For example, if a +1/+1 counter is put on a creature you control, then you cast Botanical Brawler, then another +1/+1 counter is put on that first creature, Botanical Brawler's last ability won't trigger.