Amoeba

From Softology's collection · B5-7,12-13,15/S9-26/C5

A blob that swells until it fills the box, then sets solid.

How the rule works

Each cell has 26 neighbours: every cell that shares a face, an edge or a corner with it (the Moore neighbourhood).
An empty cell comes alive when 5 to 7, 12, 13 or 15 of its neighbours are alive.
A live cell stays alive when 9 to 26 of its neighbours are alive; otherwise it starts dying: for 3 generations it fades, is not counted as a neighbour and blocks births, then the cell is empty again.
With 5 states in all (alive, 3 dying, dead), this is a Generations rule.

It starts from a random block in the middle of the box, 50% full and half as wide as the box. Each run uses a new seed.

B lists the neighbour counts at which an empty cell is born, S those at which a live cell survives, and C the number of states. How to read a rule