Will Ultraman Zero win the battle over the almighty evil forces? Ultraman Zero joins forces with his senior warriors Ultraman Dyna and Ultraman Cosmos and they transform into Ultraman Saga to stop ...

Second among my favorites would be Mefilas, although they are presented more as a being in the same vein as Ultraman (though still more monstrous) that can transform, rather than your standard Kaiju.

Zetton known as a monster who defeated Ultraman has evolved more evilly, and it seems that the likelihood that Ultraman can win is almost unlimited to zero. The package looks something like this.