They’ve already added the cast of Star vs. the Forces of Evil because they’d recruit any of the newest animated characters. The closest this can get to making sense is Star being a dimension hopper, but there’s no one they wouldn’t touch.
Except Penn Zero.
Nobody cares about the Penn Zero.
🎵PENN ZERO SLEEPS WITH A TEDDY!🎵 (I got that line from an end credits promo that aired before one episode of Star vs....
THANK L A M I A THE POOHPHILES HAVENT GOTTEN PENN YET