ThePersonInFrontOfYou
Lightning thrust and executioner are probably the best things to use, really. Surpass that off-the-wall defense. Do you have Dragon Soul for the hero? That move ignores defense too.
What levels are your characters? You might want to work on getting some better items and grinding a bit (generic advice), but if you're gonna rely a fair bit on the critical hit moves, there's some luck involved too. Metal slash is also a good idea, if you want Angelo attacking, I guess. Don't forget to raise tension.
The last thing you needed in your day was cross between a metal slime and a dragon, right?
Funny thing is, even on my mostly complete file(just need to work on skills by farming seeds of skill), everyone is level 99. So yes, Hero does have Dragon Soul. For some reason he just whiffs 90% of the time. -shrug- I don't remember if he has the wave of ice so I prefer not to psyche up just in case. My current equipment set up is pretty simple for weapons and armor and the like: Hero on the Hero Lance or Dragovian King Sword, Metal King Shield, MK Armour, and the Argon Ring, Yangus on the King's Axe(I made the Megaton Hammer...DERP) or Heavy Hatchet, Dark Robe(for evasion since he has crap evasion), some shield I can't remember off the top of my head, and the Catholican Ring, Jessica on the Gringham Whip, Divine Bustier, can't remember shield here either, and I THINK the Goddess Bracelet for her accesory, Angelo on the Shamshir of Light, a Mirror Shield, the Dragon Robe, and I can't remember his accessory. And yeah...last thing we needed was a bloody Metal Slime dragon. Then again with MY luck with Metal Slimes, why do I hate this boss so much?