A mechanism for arming / disarming a sliding part, in particular for a jumping and/or shooting toy, comprising: - a sliding part mobile in translation with respect to a base between extended and contracted positions; - releasable means (144, 154) for locking the sliding part with respect to the base; - elastic means stressed between the base and the sliding part; and - control means adapted i) to progressively store potential energy in the elastic means by displacement of the sliding part towards a contracted position under the action of motor means, and ii) to release the thus-stored energy, hence driving the sliding part towards the extended position under the effect of a releasing of the locking means, said control means comprising: - an arm articulated on the sliding part; and - a rotary part rotationally mounted on the base, controlled by said motor means and having an inner cam surface adapted to stress a finger integral with the arm during the rotation of said part, the control means being adapted to control the motor means: i) in a first mode where the sliding part is contracted via the cam surface acting on the arm through the finger, then abruptly released after the finger has reached a release area formed by the cam surface, during the same rotational movement of the rotary part, this mechanism being characterized in that it further comprises: - a lock adapted to cooperate with a locking arrangement formed on the arm, and in that the control means are adapted to selectively control the motor means: i) to said first mode, or ii) to a second mode where the sliding part is contracted via the cam surface acting on the arm through the finger, then locked by the lock acting on the arm locking arrangement, then abruptly released after the finger has reached a release area formed by the cam surface, causing the disengagement of the locking arrangement with respect to the lock during a reverse rotation of the rotary part. - a sliding part mobile in translation with respect to a base between extended and contracted positions; - releasable means (144, 154) for locking the sliding part with respect to the base; - elastic means stressed between the base and the sliding part; and - control means adapted i) to progressively store potential energy in the elastic means by displacement of the sliding part towards a contracted position under the action of motor means, and ii) to release the thus-stored energy, hence driving the sliding part towards the extended position under the effect of a releasing of the locking means, - an arm articulated on the sliding part; and - a rotary part rotationally mounted on the base, controlled by said motor means and having an inner cam surface adapted to stress a finger integral with the arm during the rotation of said part, i) in a first mode where the sliding part is contracted via the cam surface acting on the arm through the finger, then abruptly released after the finger has reached a release area formed by the cam surface, during the same rotational movement of the rotary part, - a lock adapted to cooperate with a locking arrangement formed on the arm, i) to said first mode, or ii) to a second mode where the sliding part is contracted via the cam surface acting on the arm through the finger, then locked by the lock acting on the arm locking arrangement, then abruptly released after the finger has reached a release area formed by the cam surface, causing the disengagement of the locking arrangement with respect to the lock during a reverse rotation of the rotary part.