Bahamut's Claw is always there since P1, but it was weak in that phase, P3 (heaven fall) it become 3 hit combo. on final phase it become 5 hit combo (you need CD for this) the timing for Bahamut's Claw in final phase is right after Bahamut's Favor and right after the beam thing that your team have to group up (forgot the name), then the rotation is repeat. I pop Sentinal + forsight on first one and Bulwak + Rampart on second. you can also have OT voke the boss to share Bahamut's Claw hit.

I use HG for 2nd heaven Fall, just to give healer easier time to dodge heavenfall and Super Nova. (we skip 3rd heaven on my group, if your group still have 3rd heaven fall I recommend you pop HG there if you MTing.)