User blog comment:Rij lee/In times of Desperation... use the Rumble Ball!/@comment-3119883-20121026111711

My personal opinion is the Rumble Ball enhances a Zoan's transformation abilities, helping Zoans to develop their "innate forms". Chopper, for example, needs the Rumble Ball to access other forms other than the three (Human, Hybrid, Full Animal). After the timeskip, he managed to transform into other Points (Horn, Leg, Arm, etc) I think it is just a matter of disciplined training to access other forms, only needing one Rumble Ball to transform into Monster Point. Chopper needs Rumble Ball before, because he hasn't trained hard.

Moreover, the Rumble Ball, I think, only affects Zoan. In the current arc, Punk Hazard, if Momonosuke does join Straw Hat Pirates (this is just a guess) and managed to retain his DF power (we're not sure if he can retain his power since Caesar claims that Momo's DF is a failed experiment by Vegapunk), it's pretty amazing to have another Zoan to use Rumble Ball.