Poison Water has a completely failsafe victory combo...
Max mana and the Poisonous Wave ability, learn Paralyze and max defensive bolts + High Attack/Low Attack.
The defensive bolts plus the HA/LA will counter all early attacks; if you run the strategy right you can win every match after a certain point without taking a hit.
Spam Poisonous Wave. Block any enemy attacks that you can, any uber attacks just Paralyze away (takes 9 poison effects off, but Wave can max to 10 in one round so never fear). Poisoned Death just for fun, once HP gets super high on your opponents.
Only things to worry about are Ice mages' Freeze Defend (which can K.O. if you're not careful with HP) and Burning Hill's Remove Special (which is an annoyance at best).
Got it by day 3 with $7000 in the first day.
Only took me about as many tries as dollars to get that much. E-rocket 3, near-max launcher & band, radar was only mildly helpful at best because you shoot down much too fast.
 "Book of Mages: The Dark Times"){kind=icon}
 "Hedgehog Launch"){kind=icon}