(Put it onto the battlefield under your control with a +1/+1 counter
Note: All prices come via PriceCharting, as TCGPlayer does not have listings for many of these eminently hard-to-find pieces of Pokmon-related cardboard
They get to destroy the artifact or creature of their choice and any cards of yours that happen to match it, unless they have a reason to take a shot at your hand
However, the last part of the ability will check how much life you've gained as the ability resolves, so if you've only gained 5 life this turn by the time the end step comes around, you could still gain 2 more life while this ability is on the stack in order to return the target creature card to the battlefield instead of your hand
You'll find lots of traces of strategies in here - there's some song synergy, some item payoffs, plenty of ways to heal your damaged units, and more draw than you'll know what to do with