I am by far no expert on this subject but, i thought i would share what i have learned in the past few weeks on this subject. First, not only does doing the "sweet spot" or "lock" on fod sound a little intimidating for someone new to it but, it can be. Here is a little guide that i have learned and it seems to work out pretty good. If you are planning on doing the sweet spot you need a few things first, 1. You will need holy wrath and angels of light for the top bar. 2. You will need locust swarm for the bottom bar. 3. You will need some form of troops to test with, personally i like using assassins because i have more of them. Now its time for the dreaded part, your first fod sweet spot. 1. At the very beggining try to attack first, on a rare occassion you will get lucky and get a victory. If it says defeated, thats ok, 2. Now the fun part, using those pots you bought, there are people that have different methods but mine is simple, first use holy wrath and angels of light together 6 times, then use locust swarm 4 times, making sure that both bars are even, you may need to use an extra locust swarm depending on the amount of damage you do, but a 6 to 4 ratio is average.
this is a link to a guide on the FIgure of Death epic battle. the guide was made by wulf and even has pictures!