Why does Rhizome Lurcher see itself in the graveyard as it enters the battlefield? (GRN spoilers)
Rhizome Lurcher's ability is a replacement effect, specifically the kind described in 614.1d:


  Continuous effects that read “[This permanent] enters the battlefield . . .” or “[Objects] enter the battlefield . . .” are replacement effects.


Replacement effects apply to an event before that event occurs. So replacement effects that modify a permanent entering the battlefield apply before it enters the battlefield. In Magic, objects can't be "between" zones or not in any zones, so in the situation in question, before the Rhizome Lurcher is on the battlefield, it is in the graveyard. So, it counts itself when counting creatures cards in the graveyard.