Double Big Bang on FFIV before Rosa could cure the party was quite fun at times
Speaking of FFIV:
NES - easytype
PS1 - hardtype(somewhat)
GBA - ?
I never had the privledge of playing the NES version, so I am unsure how much difference there is between hard and easytype. I just know PS1 is hardtype
FF1 origins had easy type, which was easier than the MP system of DoS by far. I didn't level a party to 99, but I remember having 40+ level 1 charges in easy type, and a black belt doing thousands of damage.
FF3 Garuda reminds me a little of Big Bang with his Thunder. At level 23, thunder is really devastating to the party in 2x form which happens often somehow. He just finds a way to cast it after my healer, then before my healer. I did end up beating him though