WolfMane, what you're missing is that the final atom doesn't need to be an operator, it can be a modifier. If you end up with "3" and a "x", "x3" will win the level. Combine three of the operators with numbers, apply them all to the fourth number, then apply the final operator.
Sometimes I get the feeling that there's supposed to be a fancy way to beat the levels, but the simple one is best. Bridge - http://www.king.com/games/splitter/viewer.jsp?w=11010016430478
The way I was able to beat the frogs (and the obsidian bats that follow) was to have mages with the cripple infliction, and a warrior (archer for the bats) with armor piercing. There may be an easier tactic, as mine required extensive skill points to get the boosts to damage and XP needed.
 "CycloManiacs"){kind=icon}
 "minim"){kind=icon}
 "More Blocks With Letters On"){kind=icon}
 "Zilch"){kind=icon}
 "Frantic"){kind=icon}
 "Splitter"){kind=icon}
 "Meat Boy"){kind=icon}
 "Z-Rox"){kind=icon}
 "Protector: Reclaiming the Throne"){kind=icon}