What counts as a creature "in play"?
This came up in a game of my own yesterday, and seeing that there was no answer here, I asked over at BoardGameGeek.

According to Matt Hyra (the lead developer of the game) Creature cards in your spell are in play as long as they're revealed.

Therefore unresolved creature cards in the same spell do count towards the resolution of Baconus the Butcher's ability. Other players' face down creatures do not count.