Yorvo enters with four +1/+1 counters on it.
Whenever another green creature you control enters, put a +1/+1 counter on Yorvo. Then if that creature's power is greater than Yorvo's power, put another +1/+1 counter on Yorvo.
If the entering green creature dies before Yorvo's triggered ability resolves, use its power as it last existed on the battlefield to determine whether Yorvo gets a second +1/+1 counter.
4 Oct 2019
Yorvo's triggered ability compares the power of the entering green creature only after putting a +1/+1 counter on Yorvo. If that counter causes Yorvo's power to be greater than or equal to the entering creature's power, it won't get a second +1/+1 counter.