Final Fantasy d20
Design creatures in Final Fantasy d20 using the principles from Monster Manual 3. The best reference for that is Monster Manual 3 on a business card. Leveling up monsters is easy: simply add +1 to their attack, damage, and all defenses, and increase their HP depending on their role. When it comes to MP, monsters come in two varieties: strong magic and weak magic. Strong magic monster have 4x their level MP. Weak magic monsters have 2x their level MP.