I like this idea! Link being a monster tamer this time around is a pretty good concept.
If you're still thinking about capture devices, there are a lot of possibilities, from the Bug Catching Net to the Empty Bottle. Or, how about his fairy/companion (if you choose to give him one) would attempt to "purify" the monster. xD
If you end up wanting to include the Master Sword, why not make it into a "Pokemon" like the monsters and you'd get it late-game? Though it might make the game too easy, being the Blade of Evil's Bane and all. xD
And nice sprites, by the way. I definitely support this. :D