Hi Sega Chief, I just obtained Omnislash and there's some ideas I want to share:
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First thing I want to say is that the battle against Zack was just magical, and it was the most epic combat I had in any RPG game.
I also loved the fact that if you are equipped with the Buster Sword, the pre-battle dialogue changes. However, I won the battle with the cheapest possible method, I just casted Bio3 on him and he died in 4 or 5 turns. This guy should be inmune to Poison, in fact I didn't cast Bio3 until my fifth try or so, cause I assumed he was indeed inmune to Poison.
About his attack repertory, I think he should be capable of using your own limits against you ( like Omnislash), but I loved the rest of them ( Consecutive Cuts, Grand Braver, Meteorain, Apocalypse, the one with the anime girl appearing... LOL
).
And finally, I have to say that It would be interesting to boost the strength of the Buster Sword after the fight in order to make it usable again, at least to equal the strength of Ultima Weapon but with different characteristics.
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By the way, where the heck is Heaven's Cloud?
Is the last item I need to fabricate Ultima Weapon.