Destroy target creature. You draw X cards and you lose X life, where X is the number of counters on that creature.
11/8/2016 Parting Thoughts can target a creature without any counters on it. You’ll lose no life and draw no cards.
11/8/2016 Parting Thoughts counts every kind of counter on that creature. Effects such as that of Giant Growth, Auras, and Equipment aren’t counters.
11/8/2016 If a creature has +1/+1 counters and -1/-1 counters on it, state-based actions remove the same number of each so that it has only one of those kinds of counters on it. There won’t be any counters of the other kind for Parting Thoughts to count.