This is a tough one since some games have ridiculously easy bosses on just the problem of having highly exploitable customization systems...

I'm going to avoid bosses that can be instant killed with Phoenix Downs, warm-up bosses, scripted battles, and bosses made trivial by overpowered end game set-ups.

1. I'll agree with Vampire. There is not much too him and he's a pretty easy breather boss in a part of the game before you even have access to all the stuff that makes the second half of the game easier than the first half.

2. Borghen - Yeah, he's kind of a joke compared to most of the game's bosses. There are random encounters in Pandemonium that are more challenging than Zombie Borghen.

3. Probably Djnn, he's not terribly difficult with the right party setup and if you use the Arctic Wind item, you can one shot him.

4. Cagnazzo - Thundaga will pretty much wipe out most of his health, even if it's coming from Tellah. Honestly, he can be taken down in like two rounds.

5. Any of the bosses weak to Death Claw which is quite a few of them. Besides them? Nerid, Triton, and Phobos who can be curb stomped by a party of Bard's using Requiem.

6. Kefka (1st battle) - Celes' Runic ability just completely stops him from doing anything for the fight and leaves him a sitting duck.

7. Honestly Proud Clod, I mean you can solo him in the Battle Arena for crying out. Other than that, maybe Rufus or Aps.

8. Edea (1st Disc) Ignoring how exploitable the Junction system makes fights trivial, you get Carbuncle in a boss fight prior to this one and that pretty much destroys her ability to do anything to you.

9. Ark - Bring Freya, steal the Holy Lance from it, equip the weapon on Freya, watch it die.

10. Half the bosses are gimme in this game but ignoring the battles where the game gives the boss a handicap or blatantly tells you the weakness, Defender X. If Tidus provokes it, the boss will just hit him with gravity, which can never actually kill him, giving your other two party members free turns to beat it up.

12. Hashmal - Compared to the Espers you fought beforehand, he's a joke. Float on your party no-sells his most devastating attack and if you've bothered with any of the Mark Hunts and Optional Esper battles, he's a breather boss in one of the game's longest dungeons. He's harder in Tactics.

13. Orphan, in addition to being weak to Death, Poison just makes him trivial. The lesson learned here is that you don't do call backs to Mystic Quest.