Also, remember, moving out of a threatened square will only provoke one AoO. So, if BBEG moves across the spiked chain fighters reach area, he will only provoke one AoO when he leaves his 1st threatened square, no matter how many more threatened squares he moves through that round. So, his movement would only provoke one AoO no matter how many the fighter is allowed each round.
From each oppenent.
You generate 1 AoO for all movement (from that opponent) - you may generate additional AoO from other opponents from movement but only 1 from each.