Parasite Colony

At the beginning of your upkeep flip a coin. If heads, put an Offence counter on this permanent. Otherwise put a Defence counter on this permanent. Until the beginning of the next end step, each creature that enters the battlefield under your control put X +1/+0 counters on it and Y +0/+1 counters on it, where X is the number of Offence counters on this permanent and Y is the number of Defence counters on this permanent.