Mandatory Once-per-turn Trigger
If target creature declares an Action: that creature is knocked Prone instead.
Prone: Prone creatures cannot perform actions. They can use an "get up" action to lose their Prone condition.

Mandatory Once-per-turn Trigger
If target creature activates an Activation effect: Manalock that creature instead.
Manalocked: [this] cannot consume its own mana or activate effects that cost mana for the duration.
If that card has an effect in this chain that would qualify, that effect fizzles.