One highly-improbable series of contrived coincidences later…
Celestia: “It wasn’t the Tantabus at all! It was–(pulls off suddenly obviously fake and rubbery mask)–Philomena all along!”
Luna: “This is getting completely ridiculous. What’s next, Angel Bunny pretending to be Grogar? Fluttershy’s evil twin masquerading as the Pony of Shadows? Two Parasprites in a Tirek costume?”
Celestia: “It wasn’t the Tantabus at all! It was–(pulls off suddenly obviously fake and rubbery mask)–Philomena all along!”
Luna: “This is getting completely ridiculous. What’s next, Angel Bunny pretending to be Grogar? Fluttershy’s evil twin masquerading as the Pony of Shadows? Two Parasprites in a Tirek costume?”