Growth-Chamber Guardian

{2}{G}: Adapt 2. (If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.)
Whenever one or more +1/+1 counters are put on this creature, you may search your library for a card named Growth-Chamber Guardian, reveal it, put it into your hand, then shuffle.

Ravnica Allegiance

{2}{G}: Adapt 2. (If this creature has no +1/+1 counters on it, put two +1/+1 counters on it.)
Whenever one or more +1/+1 counters are put on Growth-Chamber Guardian, you may search your library for a card named Growth-Chamber Guardian, reveal it, put it into your hand, then shuffle your library.

Ravnica Allegiance Promos

An ability that triggers when counters are put on a permanent will trigger if that permanent somehow enters the battlefield with those counters.

If a creature somehow loses all of its +1/+1 counters, it can adapt again and get more +1/+1 counters.

You can always activate an ability that will cause a creature to adapt. As that ability resolves, if the creature has a +1/+1 counter on it for any reason, you simply won't put any +1/+1 counters on it.