Can someone tell me if this is true?

[Mirinee]

Nope, you don't need to complete any side quest. Your friend simply meant the Amplam Umbra boss. At the final battle, you fight one twin on each side (one for Arkz, one for hunters), so Amplam Umbra only appears after you defeat both twins.

For Morgue Attack, it's not all that hard. Look for older threads in this section. Others have had problems with it too. I remember Sil'fer and Relmitos were quite difficult, so good luck. ^^

(Yey for people still playing Episode III.)

Edit: Oh bleh, I post slow.

Edit2: What, it's not a JP only card!!! That's Amplam Umbra, the final boss card. Also, there is a mistake on that quote. It should read:
To see this boss, complete both sides of offline story mode.