Commencing or ceasing control over a ridable entity causes it to lose all motion or momentum.

When initiating or halting control over a mountable entity, it forfeits all motion or momentum. Utilizing

/execute on controller

enables the identification of the entity's controller.

• For horses, donkeys, mules, zombie horses, skeleton horses, and camels, you become the controller if you ride it, the entity is tamed, and has a saddle.

• For boats, you become the controller if you ride it and are the first player to mount it.

• For pigs, you become the controller if you ride it while it's saddled and hold a carrot on a stick.

• For striders, you become the controller if you ride it while it's saddled and hold a warped fungus on a stick.
  For mountable entities like minecarts, it's impossible to be their controller.
  If any of these conditions change, the entity loses all momentum. This enables the deceleration of mobs while they fall, though it doesn't reset their fall counter to prevent fall damage. Although experimenting with this bug may be amusing, it can pose problems in certain situations. For instance, if any of these criteria change after the entity has been propelled with a slime block, it can be frustrating. Additionally, it results in camels losing all the momentum they gained from dashing.