Monster Seed Codes -

All monsters:
Enter the options screen while at the Soulin Monster ranch and highlight the "Buy Monster" selection. Then, enter R2, R1, L2, L1, R1, R2, L1, L2(2).

All items:
Press R2, L1, R1, L2, R2, L1, R1, L2(2) at the options screen.

View ending:
Press L2, R1, L1, R2, L2, R1, L1, R2(2) at the title screen.