From the opening of the game, the following 16 breeds are unlocked:

Antlan, Arrowhead, Ducken, Golem, Lesione, Mew, Mocchi, Mogi, Momo, Naga, Octopee, Pixie, Psiroller, Suezo, Tiger and Zuum.

Also, unlocked from the beginning are the subs for the remaining breeds.

Instructions on unlocking the mains are below.

DRAGON: Must be A class. You will receive the invitation on Apr 3. You will fight a one-on-one battle with a Dragon on May 3. Win and you get the password to unlock Dragons.

DURAHAN: Must be A class. You will receive the invitation on Nov 2. You will fight a one-on-one battle with a Durahan on Dec 2. Win and you will get the password to unlock Durahans.

JOKER: Must be S class. You will receive the invitation on Jan 1. You must fight a one-on-one battle with a Joker on Feb 1. Win and you get the password to unlock Jokers.

ZAN: Must be S class. You will receive the invitation on Jul 3. You must fight a one-on-one battle with a Zan on Aug 3. Win and you will get the password to unlock Zans.