I had such a rough time with Mordegon, I really did. He's not as bad as Dora-In-Grey for cheapness, but the fight is SO long that when you lose it really hurts.
First attempt I was LV58 and lasted a long time, mostly just tying to heal and buff / debuff. I was getting no DPS in and eventually ran out of MP. Figured I needed to keep him dazzled because his multi-hit physical attack can wipe out the entire party just like that, especially with his clone up. I tried again immediately and had the same problem, dazzle never seemed to land, the buffs his clone was casting on him meant Jade was doing barely any DPS, I'm constantly using two characters to heal. Another dragged out defeat due to running out of MP.
At this point I realised I needed to level, specifically I needed to unlock a move to get rid of his buffs (Rab and Sylv both had one that I knew about) and I needed some Sage's Elixers to solve my MP problems. I went straight to the casino in Octagonia, because there was a Roulette jackpot quest there I wanted to work on anyway. I head straight to the high rollers, ask the bunny girl about the jackpot and she says somebody is going to win it soon. Cool. Went on the 200s table, bet 200 tokens on 17 and... won the fucking Jackpot on my first spin
Did the Hallelujah + Electro Light trick twice and that took me up to LV66-62 with a good stock of Elixers and buff erasers unlocked. I switch Jade for Erik to exploit his DPS. Should be easy now right?
Same fucking slog. Every time I set up Erik and get ready to strike he either dies or gets his buff erased by the white orb move. This time I manage to beat the first form and get introduced to another, oh yeah that long ass battle was just the first half! Shit. I struggle through it, burning through Elixers and get both heads of this snake dragon skeleton fucker down to yellow when he hits me with "Bolt from the Blue" and wipes Gublet, Rab and Serena all in one. This is when I realise I don't actually have any Yggdrasil Leaves and can't resurrect anyone now. Boss is on yellow, maybe I can tough it out... Erik and Jade die on the next turn, then Sylv and I'm left with dumb old Henrik doing 36 damage a turn until he joins them. FUCK.
Try again. This time I barely make it four rounds when he does his multi-hit physical and KOs the wonderful combination of Hero, Rab and Serena. I hard quit out of the game at this point.
Two more attempts with Erik failed at the first stage, one where Erik never even got off an attack because he was either KOd, a gold statue or debuffed for the entire fight. At this point I'm like fuck Erik, at least Jade is going to be attacking every turn because she cant do anything else.
A lengthy fight followed, and rather than going back to the casino to buy some Yggdrasil Leaves like a rational person, I risked it. Jade turned out to be a much better DPS than Erik, I used hero to Quadra Slash constantly and if I got a free turn on Rab or Serena I used it to get rid of the clones. There was a rough moment near the end of phase two where Rab and Serena were both out of action (knocked down & paralysed) but I managed to drop the Dragon head during that turn, once that fell it was a gentle stroll to the finish line.
Eat shit Mordy.