Complete Pirate Key:
Actually, there is mistranslation that breeder said Material family + Armorpede= EvilArmor ,but it's wrong ,so it should be Devil family not Material.
I had DarkEye to breed his Armorpede to get EvilArmor. EvilArmor has quite expensive exp ,so you might want to breed your armorpede with his Armorpede that's way your Armorpede will get stronger and will have higher level cap. Giant Worm + Mad Candle would do trick to get Armorpede.
Complete Ice Key
This one has to be worst breed because it's very hard to get good breed unless you have Wild Ape that will lead to Trumpter. Almiraj + Dragon family= Wild Ape
This is rather easy because you can recruit SpikyBoy at Volcanoic Island in the Pirate World on 3rd floor as IIRC. You will get Bombcrag only if you breed your SpikyBoy and his SpikyBoy.
Complete Sky Key
Battle Arena; Closed
You will want to breed Your Dragon Family with his Gulpple to get Andreal ,so this has to be best offer opportunity to get great monster.
I would breed this with my Skeletor to get Servant. On the other hand, you may want Seprentia (need Great Drake) or Roboster (need Sabreman).
This is quite rather not good breed unless you want SuperTen (need Gulpbeast or Tonguella), Herbman (need any plant), or Healer (need any slime).
This offers many opportunities to get great monsters.
Dracolord (need Servant)
MetalDrake (need any material)
WhiteKing (need Skullgon, DeadNoble, BoneSlave, or Skeletor)
No civilization can survive without diversity ! Diversity is the key to fashion !~Josephine of Suikoden 5