Garuda

As stated by the description, the Garuda is the ultimate Bird-type monster, and as such, it surpasses all of its predecessors in all aspects. Its Phoenix Wind causes additional Fire-type damage, and its Ultimate Tornado can cause Darkness, making the party unable to hit it consistenly. And to top it off, it also has access to a Lv. 3 Stored Attack, God Bird, which can deal a large amount of damage to a party with low defense, so if you're hit with the Ultimate Tornado, heal off the Darkness, and try to get rid of it as fast as possible.