This is how Umarak finds out Twilight and her friends escaped goes in My Little Pony Transformers Bionicle: The Movie.
[Tempest Shadow turns and sees the cage is empty. Umarak suddenly approaches and also sees the empty cage. Tempest Shadow turns around to see Umarak and gasps]
Tempest Shadow: You're so quiet.
Umarak the Hunter: You let them escape?!
Tempest Shadow: The poor things just needed some air, so I just loosened the door and...
[As Tempest backs up, Umarak's shadow trips Tempest's shadow, causing Tempest to fall]
[Umarak's shadow laughs]
Tempest Shadow: I can't take anymore of this. [tears off the amulet]
Tempest Shadow: You wear this--this crazy magic object. [throws the amulet]
Umarak the Hunter: [panic] Careful with that! [catches it] If anything happens to it, I'm gonna be--! [brings out his Bone Hunting Bow Shooter and prepares to fire at Tempest but then he calms down and puts it away] Fun fact about shadow magic, Tempest. [puts the amulet around his neck and nothing happens] Can't conjure a thing for myself. Besides, the ponies wouldn't be able to defeat us anyway.
Tempest Shadow: But how will we get them back?
Umarak the Hunter: Don't worry. I already have a plan.
Tempest Shadow: But will they find out?
Umarak the Hunter: Those six ponies wouldn't be foolish enough to escape our sight, as long as we have their magic essence in this amulet.