Wyvern is a large creature and appears to have an array of different reds and purples on its structure. The body structure includes prominent muscles and two feet completed with three toes. Wyvern's wings appear to have gone through some conflict and are a bit tattered.
The best way to defeat Wyvern is to attack them in the air using attacks like Mega Flare and Ragnarok. If the Wyvern is on the ground, cast Stop and attack it. If you use Stop too early or too late, the Wyvern will be out of Sora's reach.
 Journal Entries
 Kingdom Hearts
Giant Heartless that attack from the air. They are quite swift for their size and are hard to attack, especially while they are high in the air. Counterattacking when they come down would be most effective.
 Kingdom Hearts: Chain of Memories
An enormous Heartless that hunts its enemies from the skies.
The Wyvern is agile despite its size. Upon sighting its prey, it rushes forward and attacks with a flurry of kicks.
 Kingdom Heart Re: Coded
Large, flying Heartless that drive straight at their prey from above. Unfortunately, "the bigger they are" doesn't apply here; Wyverns move fast and mean business. Hit them with magic, though, and you can reduce their altitude, bringing them down within reach of a jumping attack.