Yunalesca
OK, I've been doing a bit of 'research' with a friend, and have a nice useful hint to help you murder Yunalesca further if you get stuck with her Mega-Death trait in her third form.
In her second form, Yunalesca enjoys turning your party into Zombies and then trying to heal you. Now insane as it might sound, have one of your party members (preferably a fast party member with high hit points, like a trained up Tidus) stay Zombied. The reason being when she transforms into her third form, she'll cast Mega-Death on you. Your Zombied party member will survive to cast a couple of Phoenix Downs. You could risk a Meg-Phoenix, but that could take a toll on the actual Zombied person. It's best to have one Zombie throughout Yunalesca's form 3 so you can survive all Mega-Death attempts. If you're really smart, you'll beat up the Lady Summoner in the temple near the Calm Lands (the one that requires a chocobo to reach) and have her give you 99 Stamina Springs (I think) that double every member of your party's HP. That means that you could save a bit of time training.
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