Strategy: The fight against Magus is going to be a tough one, no doubt about
that, unless you are extremely over-leveled, say in the range of
Level 30-40. Anyway, you should know first off that the Masamune
decreases Magus's Magic Defense, so that's really good, considering
he is only weak against magic attacks, and his weakness varies from
time to time. Anyway, attack Magus once with a physical attack to
cause a message to appear onscreen telling you what Magus is weak
against. After that message disappears, attack Magus with the type
of magic that the message said he was weak against (using the
Masamune to lower his Magic Defense before you attack him with the
spell that he is weak against helps a bunch, so I strongly suggest
that you do it) to cause damage to Magus. Each time you hit Magus,
except for with the Masamune, he changes weaknesses, so be aware of
that and pay attention to the message onscreen. Also, after the
message appears, Magus will hit your entire group with that type of
magic attack (e.g. if the message says that Lightning is his
weakness, he will use a Lightning-type magic attack on your group).
Be sure that you heal everytime Magus attacks your group with a
spell after that message telling you about his weakness appears.
Frog's *Heal will certainly come in handy during this fight. If you
don't have *Heal, this fight will be MUCH harder, as Mid Tonics only
heal one party member at a time, whereas *Heal heals all party
members at once. Anyway, keep attacking Magus with the spell that he
is weak against, being sure to heal if your group's HP gets below
150. After you damage Magus enough, his weakness won't change each
time you attack him. When this happens, it means he's about to
charge up for his ultimate magic attack, DarkMatter, which deals out
about 200+ HP to your entire group, so DEFINITELY be prepared to
heal after that attack. Also, during the period that Magus is
charging up (you'll be able to tell he's charging for DarkMatter by
a message that will appear onscreen shortly after he stops changing
his weakness) for DarkMatter, you can attack him with physical or
magical attacks and damage him.
During this period, I recommend having Crono and Frog use the Dual
Tech X-Strike, while Lucca uses Napalm. After Magus casts
DarkMatter, heal up, as is he going to charge up for it again. Be
sure to get all your strong attacks in on Magus, be it magic or
physical, during the period that he is charging for DarkMatter. Keep
repeating this process until you win this rather hard fight.
J'ai la flemme de traduire par contre, en gros faut le taper avec une attaque physique, ca va te dire a quel type de magie est sa faiblesse, apres tu le tape avec masamune pour lui baisser sa defense magique et le bourriner avec la magie qui lui fait mal.
)