Melira, Sylvok Outcast is a central piece in the Melira-Pod combo, letting you sacrifice Persist creatures left and right and having them come back nonstop (and healthy as a Tarpan to boot) because of her nifty ability that just hates -1/-1 counters. She shuts down Infect and Wither too, and plays well with creatures that enter with -1/-1 counters to make them weaker (like Noxious Hatchling; with his friend Melira, he comes down as a 6/6 with Wither for 4!). However, Melira herself is not exempt to ENTERING with -1/-1 counters. Your opponent won’t be able to double-Scar her off the board, or try to use a Black Sun’s Zenith either. However, if Melira would enter with the counters… she does. Say you use Cauldron of Souls to save your Melira from a removal spell. She’ll Persist back, just like her friends, but since her “creatures you control can’t have -1/-1 counters placed on them” ability doesn’t exist until she’s actually on the battlefield, there’s nothing preventing her from entering with her Cauldron-given -1/-1 counter.