To easily defeat Fidchell, you need Wiseman with Ola repth or Phal
repth and rip maen, a powerhouse (I recommend Blackrose) and a heck of
a lot of antidotes, revives, items, scrolls, or spells that increase
magical defense, and mages souls. Give Wiseman the command first aid,
and give Blackrose the target Fidchell. when Fidchell makes a prophecy
(ex. all will tremble under my terrible will) use antidotes and the
items/spells/scrolls that increase your magic defense on everyone. If
wiseman still dies from the spells Fidchell casts, then use a revive
and mages souls. If you die, then Wiseman will revive you. Make sure
to replenish Wiseman's SP if he runs low. Continue with this strategy
and data drain.