Follow up with a proliferate effect, and you now have a total of four +1/+1 counters across those permanents, whereas youd only have three if you just played a comparable targeted +1/+1 counter effect
Based on the average power level, this means Donald Duck, Pie Slinger will become capable of banishing nearly every card in a challenge
Huey, Dewy, and Louie all have the Support feature, which can give Scrooge a much higher strength, allowing him to be successful in his challenges
Permission Denied's effect applies to all opponents, not just the player who controlled the spell targeted by Permission Denied
Also, until the swap happens, the ninjutsu card is technically in your hand
Creature - Sphinx Phyrexian Defiler of Faith Vigilance As an additional cost to cast white permanent spells, you may pay 2 life