And, from Nightmare Night and Nyx:
Quote:Nexus groaned and facehoofed. "Of course!" Twilight exclaimed, laughing and clapping her hooves. "The spell uses a pony's own innate magic to imprison them--- but colts and fillies have almost no innate magic! The weaker you are, the weaker the cage is!" Her words were proving true; a quick look around revealed dozens of colts and fillies pushing their way out of the bubbles imprisoning them. The younger they were, the less trouble they had pushing through the magical barrier. Rumble and Dinky were shouldering their way out of a bubble; Spike and Snails were struggling to pull Snips out of another by his forehooves.... while Peewee, alas, was far too magical to escape, and was left fluttering around the inside of his magical cage like a sparrow in a terrarium. Applebloom, Scootaloo, and SweetieBelle had figured out the score and took a running charge at the wall of their own cell, bursting through en masse. Twilight had the strange impression that the spell had been afraid to not let the demolition-gifted trio go...
Twilight turned her attention back to Pip and his pilfered crystal. "Yes, that crystal's perfect, Pip! Where did you get it?"
Flitter spoke up. "I stole it from the ponies in robes," she said. "I was hoping that they couldn't finish what they were doing without it."
"They must have used a substitute," Spell Nexus said. He tapped his chin with a hoof thoughtfully. "I wonder where they found duct tape and a banana at this hour...."