Complex sentence: By this time Demolition member Ax was suffering from health problems so a third member of Demolition (Crush) was introduced with the storyline being that the Hart Foundation didn't know which two members they would face until Demolition entered the arena.
Split into simpler sentences: By this time Demolition member Ax was suffering from health problems so a third member of Demolition (Crush) was introduced. The Hart Foundation didn't know which two members they would face until Demolition entered the arena.