This is part 1 of the battle with Zeromus at the Stillshrine of Miriam. This is the highest level hidden Esper that I've faced so far, with the most HP, but he is actually the easiest one I have faced so far, even easier than Zalera. What is annoying about this battle is that Magic is disabled due to an anti-magic field, which means you have to depend on physical attacks, and if you want to do big damage, use quickening chains often, though you need a good supply of ethers and elixirs. A major annoyance in this battle and indeed most hidden esper battles is the other enemies that appear during the battle, so you need plenty of phoenix downs, since Arise is of no use here (sometimes I actually prefer to use Phoenix Downs though, due to the lack of charge time.)