It would be cool if there were upgrades for all of the ninja's, and each character would get these 3 upgrades, Speed, Luck, Distance. Speed would go up to 25% and could be upgraded 5 times. Luck would be the upgrade in which the chances of getting a scroll would be increased and would be increased by 5% and could go up to 30% so it could be upgraded a total of 6 times. Distance would be the upgrade in which the Distance from the Gate would be shortened by at most up to 10 sec. each upgrade for Distance would be 2 seconds less from the gate. If you get all the upgrades you get a big upgrade in which Goliath's and Sweeper's give you 2.5x the points and avoiding Berserker's gives you 10 points (cannot be increased by multiplier). I also agree with BadMole but I'm not gonna type it all up.
I'm with alexburlton on the last part, the part with the complaint of too much for skipping missions on certain occasion's and/or the fact that it cost too much whenever you go up in multipliers all together. The price of it should not go up with more multipliers as much as it does because the challenges DO boost your ability to score allot, but not to score more coins, also, Skill = Longer Duration in Game = More Coins.
The main educational part of this whole game is that it shows you how to go back stage, sneak past security, and to use the right tool to kill and/or injure the gay blowtard
 "You are a..."){kind=icon}
 "How Dare You"){kind=icon}
 "SAS: Zombie Assault 4"){kind=icon}
 "Ninja Slash"){kind=icon}
 "The Swag Test"){kind=icon}
 "Kick Out Bieber"){kind=icon}
 "FPA: World 1 Remix"){kind=icon}
 "The Fancy Pants Adventures"){kind=icon}