Inkfathom Warlock

When Inkfathom Warlock enters the battlefield, you may put a -1/-1 counters on it.
As long as this card has a -1/-1 counter on this card, Inkfathom Warlock gains this effect: "Whenever another creature enters the battlefield under your control with X -1/-1 counters on it, you may instead put that many minus one -1/-1 counters, where X is the number of -1/-1 counters on it.