Necrovian Thirst-Slakers

Lifelink, vigilance, double strike.
If Necrovian Thirst-Slakers has a -1/-1 counter on it, it loses vigilance and double strike.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)
Please Ma'am, we're lost and it's so dark outside. Can you help us?