Isaaru saves the best for last, as Spathi is Bahamut, so you won’t be able to use your own. Despite that, you can use one of your elemental Aeons to battle with Spathi, since they can heal themselves with their respective element. Thankfully, Spathi will not attack normally, as all he will do is count down to Mega Flare, starting with five. So, you can attack like you would normally, possibly avoiding any attacks that might delay your turn. When it is Spathi’s turn and he’s about to unleash Mega Flare, use Shield with your Aeon to minimize the damage. The only time you might want to use your own Overdrive, if you have one, is at the beginning of the countdown.