this is only obtainable in moral and the true endings. in moral, weregarurumon evolves to metalgarurumon against puppetmon which is funny because weregarurumon is super effective against puppetmon whilst metalgarurumon is weak to him. so it actually theoretically makes the fight harder.
in the true ending, he evolves to metalgarurumon against azulongmon. if you get the trophy here cuz you haven't done moral yet then your metalgarurumon will be almost 40 levels below the boss as you go wtf and question the terrible boss design. if you cant win with this massive handicap... very easy exists for a reason.