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NEVER FEAR! THE FF4 GODDESS IS HERE! :p
Anyway.... Here is what I do..
For Wyvern, use the same technique that was used for Bahamut. Cast Wall. Also remember to attack the bloody hell out of it and have Rydia summon Bahamut..
As for Plague, Throw everything you can at it, since it is weak against that stuff. If you need to, then kill a character and revive it so that Plague starts the countdown again if you need more time.
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