Many-many years ago I played a game on GBC. Story is typical: boy magically transported to some strange world and is trying to find a way home. Game style: capture monster - use it to fight other monsters. Game used rings to store captured monster. I am pretty sure that the first monster he capture was a bull or bison, first (or second) town he visits was elf-style town on the giant tree. Can someone with good memory remind me what was the name of this game?