At the "General Select Screen", press Start + R1 + L2. Then, the difficulty selection screen will appear without a general being selected. Begin a game to control the Esgares Empire.

Easy experience:-  When fighting a very high level enemy, such as Cador, cast "Halo" on the creature you intend to level up, then fight him until his life drops less than 25. Hit as many x as possible for more xp, then finish him off with a level 1 monster. That killer monster will receive enough xp for 10 levels. Upgrading is possible immediately after the battle.

Upgrades:-  Not all upgrades are good, because the Rune cost goes up with it. Instead, train some units to level 20 before you start upgrading them. This way you can hold more units to train (for example: Dragon, Wyvern) Angels are an exception, since they get thrashed flat at non-upgrade, and after Arch-Angel, their next upgrade is 30 to Lucifer, the Fallen Angel. 

Gameshark codes

Super Strength Merriot 30076f6c00ff 
Super Agility Gereint 30076fbe00ff 
Super Agility Meleagant 30076fe600ff 
Super Agility Merriot 30076f6e00ff 
Super Intellegence BeauArte 300777b500ff 
Super Intellegence Carlota 3007741d00ff 
Super Intellegence Coel 3007714d00ff 
Super Intellegence Dinadan 3007705d00ff 
Super Intellegence Gereint 30076fbd00ff 
Super Intellegence Meleagant 30076fe500ff 
Super Intellegence Merriot 30076f6d00ff 
Super Strength BeauArte 300777b400ff 
Super Strength Carlota 3007741c00ff 
Super Strength Coel 3007714c00ff 
Super Strength Dinadan 3007705c00ff 
Super Strength Gereint 30076fbc00ff 
Super Strength Meleagant 30076fe400ff 
999 MP Carlota 8007741a03e7 
999 MP Coel 8007714a03e7 
999 MP Dinadan 8007705a03e7 
999 MP Gereint 80076fba03e7 
999 MP Meleagant 80076fe203e7 
999 MP Merriot 80076f6a03e7 
999 Rune Power BeauArte 800777b803e7 
999 Rune Power Carlota 8007742003e7 
999 Rune Power Coel 8007715003e7 
999 Rune Power Dinadan 8007706003e7 
999 Rune Power Gereint 80076fc003e7 
999 Rune Power Meleagant 80076fe803e7 
999 Rune Power Merriot 80076f7003e7 
Super Agility BeauArte 300777b600ff 
Super Agility Carlota 3007741e00ff 
Super Agility Coel 3007714e00ff 
Super Agility Dinadan 3007705e00ff 
Super Intellegence Camden 3007780500ff 
Super Intellegence Hula 300776ed00ff 
Super Intellegence Iria 30076f9500ff 
Super Intellegence Ulster 300777dd00ff 
Super Strength Asmit 3007721400ff 
Super Strength Camden 3007780400ff 
Super Strength Hula 300776ec00ff 
Super Strength Iria 30076f9400ff 
Super Strength Ulster 300777dc00ff 
999 HP BeauArte 800777b003e7 
999 HP Carlota 8007741803e7 
999 HP Coel 8007714803e7 
999 HP Dinadan 8007705803e7 
999 HP Gereint 80076fb803e7 
999 HP Meleagant 80076fe003e7 
999 HP Merriot 80076f6803e7 
999 MP BeauArte 800777b203e7 
999 HP Ulster 800777d803e7 
999 MP Asmit 8007721203e7 
999 MP Camden 8007780203e7 
999 MP Hula 800776ea03e7 
999 MP Iria 80076f9203e7 
999 MP Ulster 800777da03e7 
999 Rune Power Asmit 8007721803e7 
999 Rune Power Camden 8007780803e7 
999 Rune Power Hula 800776f003e7 
999 Rune Power Iria 80076f9803e7 
999 Rune Power Ulster 800777e003e7 
Super Agility Asmit 3007721600ff 
Super Agility Camden 3007780600ff 
Super Agility Hula 300776ee00ff 
Super Agility Iria 30076f9600ff 
Super Agility Ulster 300777de00ff 
Super Intellegence Asmit 3007721500ff 
Super Intellegence Cai 30076ea500ff 
Super Intellegence Dryst 30076ef500ff 
Super Intellegence Kiloph 3007700d00ff 
Super Intellegence Lance 30076e2d00ff 
Super Intellegence Lyonesse 30076e5500ff 
Super Intellegence Vaynard 30076e7d00ff 
Super Strength Brangien 30077c3c00ff 
Super Strength Cai 30076ea400ff 
Super Strength Dryst 30076ef400ff 
Super Strength Kiloph 3007700c00ff 
Super Strength Lance 30076e2c00ff 
Super Strength Lyonesse 30076e5400ff 
Super Strength Vaynard 30076e7c00ff 
999 HP Asmit 8007721003e7 
999 HP Camden 8007780003e7 
999 HP Hula 800776e803e7 
999 HP Iria 80076f9003e7 
999 MP Lyonesse 80076e5203e7 
999 MP Vaynard 80076e7a03e7 
999 Rune Power Brangien 80077c4003e7 
999 Rune Power Cai 80076ea803e7 
999 Rune Power Dryst 80076ef803e7 
999 Rune Power Kiloph 8007701003e7 
999 Rune Power Lance 80076e3003e7 
999 Rune Power Lyonesse 80076e5803e7 
999 Rune Power Vaynard 80076e8003e7 
Super Agility Brangien 30077c3e00ff 
Super Agility Cai 30076ea600ff 
Super Agility Dryst 30076ef600ff 
Super Agility Kiloph 3007700e00ff 
Super Agility Lance 30076e2e00ff 
Super Agility Lyonesse 30076e5600ff 
Super Agility Vaynard 30076e7e00ff 
Super Intellegence Brangien 30077c3d00ff 
999 HP Brangien 80077c3803e7 
999 HP Cai 80076ea003e7 
999 HP Dryst 80076ef003e7 
999 HP Kiloph 8007700803e7 
999 HP Lance 80076e2803e7 
999 HP Lyonesse 80076e5003e7 
999 HP Vaynard 80076e7803e7 
999 MP Brangien 80077c3a03e7 
999 MP Cai 80076ea203e7 
999 MP Dryst 80076ef203e7 
999 MP Kiloph 8007700a03e7 
999 MP Lance 80076e2a03e7