Unfortunately there's no guarantee that you will get Griffins in the game
Royal snakes on the other hand, if you complete the toads quest, it's almost a given, those babies rock
I also found when I hit the islands that I was continuously running back and forth replenishing my archers and swordsman, change of mindset (I love the way the game forces you to rethink you strategy) those pirates with their multi attack are well worth it.