Another quick level trick.

Put Big Bang on the guy you wanna level up. Equip another guy with a Bone or a Skull (HP lowering item).

Go to 3-2 (Peaceful Hill in Monetopia). Kill everything except the Old Man and one of the Scrabbits affected by his LevelUp ability. Summon the Bone guy and have him throw the bone at the Scrabbit. Move Maronna far enough away so that the Scrabbit won't attack her. Now, just keep on ending Maronna's turn for the 40 minutes that it takes the Scrabbit to get to level 9999. Throw something close to the Scrabbit and confine the Big Banger to it. Enjoy your 150 levels and 50 million Bordeaux.