When the holder of the Calvinball touches it to a susceptible creature, creature must succeed on a charisma saving throw of 12 + the user's charisma modifier or they are forced to obey an if/then rule of the user's choosing for up to 24 hours. The rule cannot cause immediate death (ex: if you have a thought, then you kill yourself), but it may cause harm if the dependent action the creature takes is within their control (ex: if you are about to attack someone with your sword, you attack yourself instead).

Only one creature may be under the effect of the Calvinball at a time, and the rule-setter may dismiss the rule as a bonus action. Additionally, a creature may only be under the influence of one rule at a time and the rule may be a maximum of one sentence in length. The user may not create the same rule twice.

Further, when you are in possession of the Calvinball you can see a large tiger about eight feet long which stays within 60 feet of the Calvinball. While it's simply an illusion, anyone of your choosing can see the tiger and those who focus hard may even be able to feel its fur and smell the tuna fish on its breath. The tiger mostly obeys your commands, though it prioritizes a good snooze and tummy scratch above all else. It's a magical world, let's go exploring.