You may exert Hydra Trainer as it attacks. When you do, target creature gets X/ X until end of turn, where X is the number of counters on permanents you control. (An exerted creature won't untap during your next untap step.)
{2}{G}: Adapt 2. (If this creature has no 1/ 1 counters on it, put two 1/ 1 counters on it.)