The Notice is send by an imperial Soldier which really cares after Rabanastre. He's afraid that the Wyvern may attack Rabanastre someday. He can be found in weapon shop in Rabanastre.
About 24 000 HP
Resistant to Libra,
Wyvern Lord can be found in the north-western part of Nam-Yensa Sandsea. Unfortunately he appears very close to Bagolies's nest. If you're lucky you'll manage to kill every bagoly there before the enemy takes interest in you.
This enemy is of a flying type, so ordinary attacks with sword of dagger won't be at any use now.
You'll easily get rid of him casting twice berserk and healing the tank. You should cast berserks on Bathier and Fran and use someone with strong white magick to keep them alive. The fight will be over before you can notice.
His attacks are: ordinary ram, Gust damaging one enemy with the power of Wind, Aero damaging everyone in range with the power of Wind and Breath attack with the element of Fire damaging every one that stand exactly in front of him.
Bounty: 1000 gil, Longbow, Shell Shield