If enough -1/-1 counters are put on Hei Bai at the same time to make his toughness 0 or less, his last ability will see all of the +1/+1 counters he had when he left the battlefield as well as the -1/-1 counters he had, and an equal number of each of those types of counters (plus any other applicable counters) will be put onto the target creature
Wait, sorry, that fact was about mongooses
What set is owyn, Lady of Rohan from
In Commander, there are a number of legends and other payoffs that reward you for playing on your opponents turns
1019 | Exile the top two cards of your library
These colors include some of the most backbreaking creatures ever printed, like Collector Ouphe, Aven Mindcensor, and Dauthi Voidwalker